# Weekly nutrient consumption in planted aquarium



## Marcel G

I would like to share with you the results of my three-months experiment with *real  consumption of nutrients* in planted aquarium.

I weighed the plant biomass (live weight) which were produced in my aquarium regularly (after each trimming). Every time I did some trimming in my tank, I thoroughly shook the water down from plants and weighed it on a digital scale with an accuracy of 0.01 g. This way I monitored the biomass gains for 3 months, and finally I calculated the average weekly biomass gain: *12 grams of live weight* for the area of about *35x35cm (60L)*. So each week approximately 12 g of plants grew up on an area of 35x35cm. Since this is a "live weight", in terms of dry matter that makes about 10% = 1.2 g of dry weight. And since we know that there is about 45% carbon (C), 2% nitrogen (N), 1% potassium (K), 0.2% phosphorus (P), and 0.02% iron (Fe) in plants' dry matter, it's relatively easy to calculate the actual amount of nutrients that plants needed for 12 grams of biomass per week: *2 g CO2, 1.8 mg/L NO3, 0.1 mg/L PO4, 0.2 mg/L K, and 0.004 mg/L Fe*.

I will add that in my aquarium, I use quite *strong light* (100-120 µmol PAR at the bottom), nutrient-rich substrate ADA Aqua Soil, I supply about 4.7 g of CO2 per day, fertilize as needed, and each week I change 50% of water. Details of the aquarium can be seen in my presentation (Nano 4).

I will definitely continue doing similar tests (and perhaps some other users will join me to have more data from different tanks), but even so, I'd say that I came to quite interesting findings => that even a relatively densely planted aquarium with strong lighting and plenty of nutrients does not need weekly more than 2 mg/L NO3, 0.1 mg/L PO4, 0.2 mg/L K, 0.005 mg/L Fe. Moreover, from the weekly dose of CO2 that I'm adding into my tank (4.7g x 7days = 33 g), the plants actually consume only 1/16.

Compare this with the amount of nutrients you supply weekly in the aquarium using different *commercial fertilizers*, if you stick to the recommended dosage:
ADA = 1 mg/L NO3, 0.5 mg/L PO4, 25 mg/L K, 0.05 mg/L Fe
Easy-Life = 2 mg/L NO3, 0.1 mg/L PO4, 5 mg/L K, 0.2 to 0.5 mg/L Fe
Tropica = 6 mg/L NO3, 0.3 mg/L PO4, 1 mg/L K, 0.07 mg/L Fe
PMDD = 1-5 mg/L NO3, from 0.1 to 0.3 mg/L PO4, 3 mg/L K, 0.1 mg/L Fe
EI = 30 mg/L NO3 (= 15-times more), 3 mg/L PO4 (30-times more), 10 to 20 mg/L K (50-100-times more), 0.5 mg/L Fe (100-times more)

_PS: The above test doesn't take into account the increase in root biomass (only partially), which means that the actual nutrient consumption will be slightly higher. Some nutrients in the aquarium will be produced naturally in mineralization (conversion of organic matter into minerals) or may be present in the substrate, which means that the plants may get by with a smaller amount of added nutrients. On the other hand, the efficiency of nutrient distribution will certainly play some role also, as this efficiency will never be 100%, so for this reason it can be wise to use little more nutrients._

Also, it's quite a known fact that the amount of _*phosphates *_have a huge influence on plant growth. When I limited phosphates in my fertilizing regime, my plants grew very slowly (perhaps only 5 g body weight per week) even under very strong light. But once I increased the concentration of phosphates to 2-3 mg/L PO4, the weekly gains increased to 25-30 g of live weight.

My point is not to save some small amout of fertilizer, but rather to understand _*what amount of nutrients our plants really need,*_ which in turn will help us to understand the usefulness or uselessness of some methods of fertilization. A lot of people grop in what fertilizing method (ie. which fertilizer) to use. As I stated above, different fertilizers have different composition of nutrients. If we know how many nutrients plants can consume under certain conditions (strong vs. weak light, lot vs. little PO4, lot vs. little CO2, etc.), we will know quite precisely what is appropriate dosage. As I demostrated on the example of my aquarium (strong lighting, lots of CO2), _*my plants will get by even with an extra-poor fertilizer*_ like ADA, which still contains enough of everything, except nitrates, because the ADA relies on the fact that nitrogen compounds are already present in great numbers in ADA substrate (+ something is being produced in aquarium from fish). Virtually all fertilizers (except EI) use relatively moderate concentrations of nutrients ... but _*these levels are still several times higher than our tank will in most cases need*_. So although I would use Tropica fertilizer in my aquarium, still the plants there will have a galore of nutrients (= practically non-limiting amounts). _*EI method *_in this regard_* is completely "overstated"*_ because it uses 15-times higher amounts of nitrates, 30-times more phosphates, ~100-times more potassium, and 100-times more iron ... than my plants need. As I said, with large quantities of phosphates the plants will grow faster, but _*is it desirable*_? I know no one (except the people who make a living selling plants), who would want each week throw away a bucket of plants. So my conclusion: Methods like EI and PPS-Pro are designed more for the avid plant growers; in normal plant aquarium I would probably not recommend them to anyone (although I was formerly rather their advocate). And the argument that excess nutrients has no effect on algae, I do not consider valid. It's certainly reasonable to use a little more of fertilizer than is the "real" consumption, because the effectiveness of its distribution is certainly not 100% (due to imperfect flow; part of the micronutrients deteriorate before it gets to the plants, different plants have different demands, etc.), but how much more ... 2- to 3-times more? Definitely it's not necessary to use 100-times more.

I know that many EI advocates will argue that larger amounts of nutrients don't pose any risk (although I don't think so). Still, it can be useful to know what's the real nutrient consumption in our tanks.


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## Martin in Holland

Even if EI is 100x more than needed, it is still 200x cheaper.....
Anyway, what you are saying is that we could use EI, but a lot less of it?


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## pepedopolous

I think it's well known that EI is all about over-supply. Got me thinking though... if plants need such small amounts, why should we dose EI macro and micro ferts more than once per week?

P


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## Tim Harrison

EI was never meant to be rigidly applied...http://www.barrreport.com/showthread.php/4882-Confusion-about-EI-and-other-myths nice little study though...


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## Marcel G

EI was never meant to be applied rigidly ... but did you know that most people (who are using this method) are dosing probably 50- or 100-times more nutrients then needed? Do you know that all these people believed Tom Barr's estimate ... but it seems that this estimate is extremely overestimated?! Tom Barr never mentioned elsewhere how he figured out, that this amount of nutrients is the "sweet unlimiting spot". I just marvel at why no one ever questioned these amounts. If it's true that most planted tanks have such a low nutrient consumption, then why to dose 100-times higher amount if 5-times higher amount would be "unlimiting" in the same way? Why? Because it's still safe for critters? Or because I have not a better idea (better estimate)?

When I dose 4 mg/L NO3, 0.2 mg/L PO4, 0.5 mg/L K and 0.01 mg/L Fe weekly in my heavily planted tank with extra strong light, high stable level of CO2 and ADA substrate, then I'm already using "EI" method.

I don't care what other people are adding to their tanks. If someone wants to add 100 mg/L NO3 or 30 mg/L PO4, its his choice. My goal in doing this test was to find out what my plants really need. Based on this I can supply them with enough nutrients without going to extremes and creating "nutrient solution culture" for algae.


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## Martin in Holland

I am using EI as much as you mentioned...here is the thing, I had some problems before with GSA so I dosed more PO4 and indeed it helped, I also had some BGA so I dosed more NO3 and this also helped. If we dose too much than how is this possible?
I'm not trying to attack you in any way, I just want to understand.


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## Marcel G

There is a difference between what plants may need, and what can inhibit algae in one way or another. So while plants get by with such a small amounts of nutrients, in case you have GSA problems, then it's maybe wise to add more PO4 (and the same logic applies to BGA and NO3). I did not want to say that people should decrease their dosages (as I said, it's entirely their fight - their choice). Do whatever you want. My point was just to show the results of my test, to show that our plants probably don't need 100-times more nutrients like EI suggests. So if you dose more PO4 ... you do it for eliminating the problems with algae, not to supply your plants with enough nutrients. So if someone suggests using higher levels of nutrients (like PO4 or NO3), it's not because the plants really need it, but because algae hate it.


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## Martin in Holland

Good point


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## pepedopolous

ardjuna said:


> Tom Barr never mentioned elsewhere how he figured out, that this amount of nutrients is the "sweet unlimiting spot"



If I recall correctly, Tom added progressively more and more nutrients to an aquarium with an insane amount of lighting and CO2,
to the point where adding any more nutrients did not result in any increase in growth.


P


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## Crossocheilus

What I am about to say is NOT based on any science or experimentation or experience,  just a thought....

Perhaps the plants only actually use a small amount of the mineral ions we provide, however it is the availability of them in the water that means that they never have a lack of it. 
E.g.
If all they need was 2ppm of nitrate and all that was in the water was 2ppm of nitrate then the nitrate that they needed, although enough was present, would be scarce and thus not always available exactly when and where it was required? By having an excess in the water column at any given leaf their is an abundance of, in this case, nitrate. This means that nutrient uptake is very efficient and the plant or part of a plant is never left without any (nitrate)

Although come to think of it good flow should prevent that problem (?)

Sorry if that makes no sense or is of no help...


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## Michael W

In this article http://www.barrreport.com/showthrea...I-can-get-you-there-with-a-small-modification Tom Barr commented on dosing only what is needed for plants to grow but observing the change in the plants growth. He suggests that you can dose the standard EI and lower the amount until you reach a point where you see the plant show signs of struggle, you then gradually dose more to find an optimum level which will encourage growth without over dosing every time.



Crossocheilus said:


> Although come to think of it good flow should prevent that problem (?)



Good flow helps a lot of problem and you mention a really good point. If someone can't achieve a nice flow, plants may not do well in receiving the nutrients, a way around it would be to dose more and hope for the chance of contact between nutrients to increase to compensate for flow.

I use the duckweed index proposed by Darrel to dose my low tech tanks, which is similar to the method I linked posted by Tom Barr except you monitor the growth of floating plants and dose if the floating plants don't look so good. This is effective because floating plants receive more light than those fully submerged, they have access to unlimited CO2 therefore, the limiting factor to their success is nutrients.


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## Tim Harrison

I think that Tom also mentions that EI can be fine tuned...the dose can be steadily reduced until the signs of deficiency occur and then notched back up to the previous dose. 

Edit: Thanks Michael that's the link I was looking for when you posted, and beat me to it.


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## Marcel G

pepedopolous said:


> If I recall correctly, Tom added progressively more and more nutrients to an aquarium with an insane amount of lighting and CO2, to the point where adding any more nutrients did not result in any increase in growth.


I cannot imagine how he could do that ... how he could find this out. How was he doing such a test? Tom Barr is very taciturn as far as explaining his methods/methodologies. BTW, is anyone of you using "insane amount of lighting and CO2"? So even if I admit that his nutrient estimate (EI) could be valid for some extreme situation, my situation was definitely different ... although I was using 120 µmol PAR in my test, and high levels of CO2 (also in my tank, the dissolved organics are virtually undetectable according to the lab analysis, the dissolved oxygen level is around 10 mg/L during photoperiod, the flow is good, most of my plants are pearling). What light should I use so that my plants will need 15-times more NO3, 30-times more PO4, and 100-times more K and Fe? 700 µmol PAR at the substrate? Is 700-1000 µmol PAR at the substrate a normal environment in our tanks? Absolutely NOT !!! *So why should I follow that estimate (EI) if the conditions on which it is based are absolutely unrealistic?*


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## Crossocheilus

Because no matter how many plants you have or how ever high your lighting is you will NEVER run put of nutrients meaning plants never get deficiencies or stunted growth, as a whole plant or as one cell.


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## Marcel G

Crossocheilus said:


> Because no matter how many plants you have or how ever high your lighting is ...


So if I understand that correctly, I should put into my tank whatever Tom Barr says, because he says that my plants will never be limited at these amounts. Well, then I have another estimate for you: _*Eat 50-times a day, and eat really big portions like professional bodybuilders ... because if you eat that amount of food, you'll NEVER be hungry !!!*_ This is exactly the same logic. No matter that you're not any professional bodybuilder, no matter that you NEVER burn such a high amount of calories ... just do it !


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## Michael W

I don't follow the EI guidelines but to me EI lets you get away with over dosing. It allows flexibility and really It doesn't make a lot of hassle, just drop some salt in and that is that. As far as I can see Tom Barr doesn't dwell on specific measurements, he proposes his dosage but I don't see him just advocating them, he has written different methods of dosing to suit the needs of the hobbyist as seen in the link I had provided.


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## Tim Harrison

ardjuna said:


> So if I understand that correctly, I should put into my tank whatever Tom Barr says, because he says that my plants will never be limited at these amounts. Well, then I have another estimate for you: _*Eat 50-times a day, and eat really big portions like professional bodybuilders ... because if you eat that amount of food, you'll NEVER be hungry !!!*_ This is exactly the same logic. No matter that you're not any professional bodybuilder, no matter that you NEVER burn such a high amount of calories ... just do it !


Not sure that's a particularly good analogy...but I guess it is easy to misunderstand the principles of EI, I know I did at first, but if you read the links posted above I'm sure you'll gain a better understanding.


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## Marcel G

Troi said:


> If you read the links posted above I'm sure you'll gain a better understanding.


If you read my first post I hope you'll gain a better understanding of my point.


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## Marcel G

I'll comment some sentences from the barrreport.com (see post #11 by Michael W):



> EI is somewhere about 1/4 the way past the Critical point for most aquariums, maybe a very high light tank might have a critical point of normal EI dosing.


1) First of all, Tom B. says that for most aquariums the critical point is somewhere about 1/4 EI, and that very high light tank might consume as much nutrients as EI supplies. Do you think my tank uses a "very high light"? Do you think that 120 µmol PAR at the substrate (and about 400 µmol PAR at the surface) is high enough? I would think so. But maybe I'm wrong. So how it is possible that even under such a high light my plants consume only 1/15 of NO3, 1/30 of PO4 and 1/100 of K and Fe?



> If you need to test CO2 and or light, you need a method to make sure there is no dependencies on nutrients, EI is the best and frankly the only method that suggest that approach.


2) What a humble statement! Tom B. thinks that EI is the only method ensuring an unlimited amount of nutrients. If my plants need only 2 mg/L NO3, 0.1 mg/L PO4, 0.2 mg/L K, and 0.004 mg/L Fe weekly ... and most commercial fertilizers supply more than that ... does it still mean that the only method ensuring unlimited amounts of nutrient is EI? Hardly!



> Leaner methods end up stunting or slowing growth and you never know what the good growth independent of nutrients even looks like, this is bad for a hobbyist interested in growing plants well.


Do you really think that adding less then 15-times more NO3, 30-times more PO4, 100-times more K and Fe is bad for hobbyists? Do you think that 5-times more NO3, PO4, K, and Fe is not sufficient for good growth?


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## parotet

Subscribed... This discussion is extremely interesting. Thanks Marcel for sharing your results. Looks like a lot of work has been done. Will you include an extended version of this experiment in your website? This is a promising thread!

Jordi


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## pepedopolous

Another thing about EI is that I think Tom Barr was also aiming to make a fertilisation method that makes test kits unnecessary. Previous methods like PMDD were requiring hobbyists to aim for specific levels of nutrients which are actually impossible to accurately measure using consumer-grade test kits. Also previous methods promoted the absolutely false idea that phosphates and excess nutrients in general = algae.

But as someone who has recently been considering buying an expensive dosing pump, this thread makes me reconsider this idea. If plants use as little nutrients as Marcel's experiment suggests, why not simply add some macro ferts and micro ferts once a week after a water change and forget about daily dosing? Even using heavily-diluted EI it's still unlikely that plants will run out of nutrients.

It has to be said that the number one problem people have with their aquariums is getting good CO2 levels/distribution. Ferts are much easier to get right whether using EI or ready-made products like Tropica's.

P


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## Crossocheilus

I do get what the OP means:
Why dose that much if it is totally unnecessary? 
I suppose it is so cheap and doesn't harm fish so there is nothing wrong with dosing excess. 
I think we need an expert on aquatic plant biology to say whether the concentration is linked to the amount used.

Does high concentration benefit low requirement?

Does low concentration limit low requirement?


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## Martin in Holland

Here is another food for thought, if I overdose my garden plants, it will result in burns curling leaves and other strange undesirable growth, why doesn't this happen to my plants in the tank, even not the floating once or the plants that grow out of the water?


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## Ben C

One quick question ardjuna - how did you ensure you were only ever removing NEW biomass each week?


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## Marcel G

Crossocheilus said:


> I think we need an expert on aquatic plant biology to say whether the concentration is linked to the amount used.


+1 Right on target (I would like to know that as well.)
Still, I remember that in rivers the amount of nutrients is extremely low (like µg/L, not mg/L as in our tanks), and still the plants grow well. But it would be interesting to find out, how much nutrients will flow through the river in a day ... how much nutrients the plants have at its disposal each day. I'll try to ask some expert at the Faculty of Science.



Ben C said:


> How did you ensure you were only ever removing NEW biomass each week?


I did ensure this in a statistical way. I tried to keep my layout the same throughout the 3-months test. Then I trimmed the plants when the layout changed too much. Then I weighed the biomass. Sometimes I did pull out some plants even with their roots, cut them in half, and replanted the stems. Doing this for 3 months period I would say that I can get quite accurate picture of the biomass increase. But as I noted in my first post, it doesn't take fully into account the root biomass gains. Still, this is according to my opinion much more accurate method for finding out the real nutrient consumption, then using test kits and measuring the concentration of nutrients on the beginning of the week, and then at the end of the week (because a lot of nutrients will end up in substrate, filter or other non-plant biomass). So I know about the limitations of this method, but if other hobbyists can join me in this test, then we could have much more data, and thus much more accuracy (under different conditions).

This is my tank where I did the test:


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## parotet

Hi all

Not an expert on plants' physiology so not sure if the methodology used and some assumptions made are solid enough for reaching these conclusions. Nevertheless there is something which has always amazed me and was discussed some weeks ago in this thread

http://www.ukaps.org/forum/threads/sacrilege-i-know-o.34536/

And of course in other threads. It is the fact that thousands of aquascapers use ADA, Tropica or other fert systems with excellent results, and as mentioned before they include much less nutrients than EI standard dosing. In the link included above the 'enriched soil' issue is also discussed (there's usually an automatic answer from someone saying that ADA system relies on Aquasoil enriched soils) but ADA aquasoil is widely used by hobbyists that follow both approaches: super excess of nutrients (let's say EI approach) and slight excess of nutrients (ADA, Tropica and other formulae). In other words, using or not a soil that is able to release nutrients to the water column, both systems work (probably the ADA system which includes the less nutrients would need extra doses, not sure). A good example for me is the Tropica ferts range used successfully and extensively by members of this forum with and without enriched substrates. It is true that the problem with commercial ferts is that folks follow the instructions without taking into account that it is just an average recommendation but that needs to be adapted to the tank conditions (light, biomass, etc.), resulting sometimes in a lack of nutrients. EI avoids this situation making sure this won't happen, and that no effects will be noticed in the tank (algae blooms). So it is really a method for the layman.

So independently of Marcel's experiment accuracy (anyway thank you for making this effort) I guess there is some evidence that there is a kind of safety margin that would be interesting to be explored in detail. Most of us just follow others' experience or advice but we do not create our own evidence (actually this is a hobby, most of us grow plants for pleasure not for demonstrating anything).

The question IMO is how large this safety margin we need is and what are the parameters that may influence it. I'm sure light is one of the main ones, also co2 optimum performance or substrate (aquasoil at the end is, as mentioned many times, a safety margin). So once again, this is an equation with interdependent parameters and this safety margin that can be considered large enough is not maybe that much if other aspects are not addressed correctly.

Jordi


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## Jake101

I think the more important question is the minimum required concentration of any specific fertilizer in the water column. This naturally depends on other factors (lighting, co2, nutrients in the substrate, temperature...) and is different for each species and probably varies a bit between individual plants (size etc.)

Anyway, I am not a plant physiologist, but I would guess that the concentration of ferts required in the water column while having excess of co2, high level of lighting and inert substrate is much higher than the actual calculated amount according the increased dry weight of the plants.


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## parotet

Hi all

I have two questions I would like to ask to Marcel.

1. You are quantifying the amount of co2 used in your tank in grams. I would like to know how you did it. 

2. You mention that dissolved inorganic were undetectable in your tank even you were using a high amount of light. I'm probably missing something but as far as I know they come mainly from plant metabolism or dead tissues (not taking into account fish to make things easier). Do you link this very low dissolved organic levels with a lower amount of nutrients' excess in the water column? (Maybe I'm completely wrong but when I have doubled my EI dosage (to make sure I was not having fertilization problems) I have noticed an increase in surface oil... Can bacteria on surface films use this super excess of nutrients?) The only other explanation I can imagine is that the strategy of PO4 shortage decrease growth rate and therefore metabolites released as by products to the water column.

Jordi


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## Marcel G

#1) I have a calculator on my site (http://www.prirodni-akvarium.cz/en/index.php?id=en_co2calc), where you can calculate the volume of CO2 after filling out the input parameters. So if you know a diameter of one CO2 bubble, number of hours you bubble each day, and number of bubbles per second, you can easily calculate the volume of gas. In my case it's 2.4L CO2 per day. And given that 1 g CO2 = 0.506 L, you can get to the result of 2.4L x 1 g / 0.506 L = 4.7 g CO2 per day ... if I'm correct.

#2) Dissolved organics (measured as COD) where < 0.50 mgO2/L according to the laboratory analysis. Maybe COD is not the best method to measure organic pollution in a tank, or maybe the products of photosynthesis do not contribute that much to this kind of pollution, but that's how the lab results ended up. BTW, I too have a surface oil in my tank each day, but I use skimmer to clean it.

PS: In a couple of days I'll publish an article about my test results.


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## roadmaster

Well,
I'm wondering how root biomass is not weighed into the equation.(do not nutrient's feed these too?)
Perhaps your particular species of plant(s) has much more capability to store nutrient's in this root biomass for lean times, and thus less is needed in water column??
How can you not weigh the possibly increased root mass when measuring dry weight /liveweight of plant's you pull up to measure same?
How many species of plant's out of the several hundred were test's run on?
How many folks I wonder are interested in how lean they might be able to run nutrient level's to achieve desired result's as opposed to running rich on nutrient's and eliminating any possibility of nutrient deficiencies?
Leaves only CO2 and light to worry bout.
Define your idea, or possibly provide photo(s)? of what you deem to be densely planted tank which I should think would have more than a little influence on how much or how little nutrient's are needed for same densely planted tank(s).
What were temps in test tanks which might have affected nutrient uptake if one believes lower temps = lower metabolosim's/rates of uptake. ?
Why does it appear that EI work's so well for the masses from both low tech and high tech?


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## Marcel G

Well, I did not say I did not measure root biomass at all. I measured it but only when I uprooted whole plants. I did the test in my planted tank, and I did it for 3 months. How should I do it with accounting root biomass withouth devastating my whole tank?! If you can do better, just do it, and don't criticize only. And in the post #25 you can see the picture of my tank (for your information). And if you doubt on the results published, please, give me your data! Did you weighed some sample of aquatic plants to have some idea? Maybe you'll find out that if you take different plant samples and weigh them, the results will be quite similar for their dry mass. Still, even if there will be some difference, the results won't be so different (say 1 mg/L NO3 vs. 3 mg/L NO3). But I hope you give me some better data.
PS: Why does it appear that PMDD or Tropica ferts work so well in so many tanks? I hope you answer me this question.


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## roadmaster

I fear I am unable to comment on PMDD or Tropica ferts for I have not tried these.
I have noted,, different methods of growing aquatic weeds produce for different folks, without denigrating other methods or people such as Tom Barr.


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## dw1305

Hi all,





Jake101 said:


> I think the more important question is the minimum required concentration of any specific fertilizer in the water column. This naturally depends on other factors (lighting, co2, nutrients in the substrate, temperature...) and is different for each species and probably varies a bit between individual plants (size etc.)


 I think that is probably the relevant point, as long as there is that minimum concentration of all of the macro & micro-nutrients some plant growth will occur.

Aquatic plants are just like terrestrial plants, you have some highly competitive plants with huge potential growth rates under eutrophic conditions, and some plants which are adapted to survival in very low nutrient conditions.

Adding nutrients will make _Anubias, Bolbitis  _etc grow a little more quickly, but not a great deal more, and low nutrient conditions will be unsuitable for _Lemna etc.  _If you want a terrestrial plant analogy it is the difference between growing tomatoes and orchids.





ardjuna said:


> Dissolved organics (measured as COD) where < 0.50 mgO2/L according to the laboratory analysis. Maybe COD is not the best method to measure organic pollution in a tank, or maybe the products of photosynthesis do not contribute that much to this kind of pollution, but that's how the lab results ended up.


 I think you are right, COD is just too blunt an instrument for relatively clean water, it is really designed for polluted situations. A 5 day BOD value would be better, or you could use conductivity as a proxy, but it will only give you a ball park figure.

cheers Darrel


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## Marcel G

dw1305 said:


> I think you are right, COD is just too blunt an instrument for relatively clean water, it is really designed for polluted situations. A 5 day BOD value would be better, or you could use conductivity as a proxy, but it will only give you a ball park figure.


I was told that BOD is part of COD, so if COD is low, then BOD should be even lower.
So BOD measures just levels of biologically active organic matter, while COD measures everything that can be chemically oxidized (including biologically active organics).


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## dw1305

Hi all,





ardjuna said:


> I was told that BOD is part of COD, so if COD is low, then BOD should be even lower.


Yes that is right, but COD gives you a very broad brush picture. In COD, basically you burn out all the organic matter with a known volume of  (usually) potassium dichromate (K2Cr2O7), there must be sufficient oxidising agent so that when you have finished the reaction you have some remaining. You titrate this solution against FAS (NH4)2Fe(SO4)2·6H2O (and an indicator) which indicates how much dichromate was left (to be reduced  to Cr+++ ions).

COD gives you a quick estimate of pollution, and usually you would use it to answer a question like "_which one of these sources was polluted with milk/silage liquor/sewage/slurry_" after a fish kill in a river etc.and  you might use COD in conjunction with bioassay organisms if you thought that pesticides may be involved. In the pesticide scenario you would have a low COD, and a low lc50 value for the bioassay organism.

If you wanted to look at low level pollution you would use 5d BOD and a biotic index. This is because it is possible to have a relatively low COD in streams etc, but still have times when BOD exceeds dissolved oxygen supply, which is why you need the biotic index as well.

cheers Darrel


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## Marcel G

roadmaster said:


> different methods of growing aquatic weeds produce for different folks, without denigrating other methods or people such as Tom Barr.


OK, so you are commenting my methodology and findings, and blame me for denigrating other methods or people. But did you ask the same critical questions Tom Barr also? I hope that you did. I hope that you are equally critical to all methods and methodologies. And, please, can you share with me the answers all these people gave you about their methods and methodology? I was never reading any methodology by Tom Barr or any other person. The only thing I'm trying to do is to find out the average consumption of aquatic plants under some defined conditions. If you read all this thread you may better understand my objections to methods like EI. I know, of course, the limitations of my methodology => it's not just partially neglecting root biomass, but the exact ratio of nutrients in dry mass (which is different for different plant species) + the percentage of dry mass (I count with 10%, but it may be from 5 to 30% in some species) + temperature (as you already mentioned) + efficiency of distribution and nutrient uptake + light, CO2 and phosphates (each could be limiting to growth rate) also ... and maybe some other factors. I don't try to hide any factors. I'm just seeking some answers, and do it frankly ... unlike many others. I just wonder how easily people are able to take some statements without judging them.

I would like to encourage you to try other methods (not just EI). You would be surprised how little nutrients are needed for planted tanks to prosper and flourish.

PS: My concern is not to criticize other methods (like EI) although I have to say that EI is according to me totally out of reality. My goal is just to find out the average consumption of plants in average planted tanks with average conditions. I'm glad if anyone give me a constructive criticism. But if someone criticize without giving any better ideas or without showing any relevant data, then it's just hypocrisy in my eyes.


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## ian_m

Fantastic that you should try this experiment, but I think your method of weighing only the plant mass is fatally flawed, though good at a first pass testing/falsifying EI. Please don't shoot me....

Other sources of error are:
- You do mention root mass, I think you will find is bigger than you think.
- Plants take in the H from water to make carbohydrate, another source of mass you haven't accounted for.(maybe not a lot),.
- Plants use energy at night give out CO2 and other waste products.
- The major source of error, I think is, plants in such high light conditions evolve a huge amount of excess organics, which are built from your CO2 and ferts. These organics don't always stay in the water column as a measurable quantity and your filter & associated bacteria will take a lot of this out. I am quite surprised the amount of detritus collecting in my filter, far more than my fish can poo.

So I propose this method of testing ferts consumption.

- You dose the water with you accurately measured quantity of ferts.
- You accurately measure the amount of left over ferts in the water after each day/week/month.

This will give you actual consumption figures based on knowing how much you put in.

You know the main problem with this, is testing the levels of left over ferts.

Could water from the tank be evaporated leaving solids (ferts and organics), heated to "burning heat" to carbonise the organics (assuming left over ferts don't decompose) and ferts redissolved in water, evaporated again and weighted. This is making the assumption organics in the water are significant and when burnt are insoluble.

This would at least give an approximate amount of all the ferts left over.

Just my 2p worth.


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## Marcel G

These are very interesting points! Thanks for your comment. I have to think of it.


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## parotet

These last comments are very interesting! This thread looks promising. Unfortunately I am not able to suggest any better methodology but I have spent quite a long train journey today comparing fert dosing in the Tropica website (see 'inspiration' section where all the tanks specs are given) and the standard EI dosing. All the tanks included in the advanced category (high light, high co2, demanding plants) do use higher doses than recommended (from 1x to 5x) but even though the ppm released to the water column are much lower than for EI methods. There are even some awesome layouts from Mark Evans using Aquasoil in which no macros were added (just Tropica Premium). All of them use high levels of Co2 ( we all agree this s key aspect), the difference in NO3 for both methods are significant but not always, but what makes really the difference is the huge difference concerning PO4... Really huge difference. PO4 is said to boost plant growth, so I guess plants demands regarding the rest of nutrients.

In other words, independently of technical aspects regarding the methodology used, I think that all EI users are aware that lower nutrients systems do work. Is it right to assume that low nutrient dosing systems are based on limiting Po4 and that this will reduce automatically NO3 and CO2 needs? This will be quite useful (if it is true) as less growth would be compensated by less co2 demand thus larger safety margin for the most critical aspect in high light planted tanks management.

Jordi


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## Marcel G

Jordi, I'm 100% sure that PO4 is the bottle neck in most cases. By PO4 you can control the growth rate very well. In my test, when I lowered the PO4 dosage to 0.1 mg/L per week, the biomass (live weight) was just around 5 g ... vs. 20 g when I added 3 mg/L PO4. So it's known fact that by limiting PO4 you can slow down the growth rate successfully without making plants suffer.


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## Marcel G

ian_m said:


> Other sources of error are:
> - root mass...
> - H from water to make carbohydrate...
> - waste products...
> - huge amount of excess organics...


I have to find out some relevant data to these potential errors, but as I already said, I did weighed the root mass in some cases, and in other cases we could use some average coefficient to account for this ... when we find out what's the average ration between stems and roots. Also consider this: If I trim some plants with huge root mass, do you think that the plant have to make a new roots for the new stems? I would say that once the plant makes its root system, the roots will not grow to infinity, so when you cut off the stem, (maybe) the roots will be the same and don't grow any further because you just cut the plant in half and it needs no such a big root system any more. But I'll try co ask these question to some experts.

As to the waste products I remember to read somewhere that the by-products of photosynthesis in macrophytes could be up to 10%. To be honest, this number doesn't seem to be so big. If I find out in my test that my plants will use up say 3 mg/L NO3 per week, then 110% (3.3 mg/L) will make nearly no difference.

But as I said, I'll try to find out some scientific data to account for these things.

Your supposed method of testing ferts consumtion is much more erroneous according to my opinion. Once I dosed ~30 mg/L PO4 into my tank. The second day I measured 5 mg/L PO4 in there, and the third day I measured 0,0 mg/L PO4. Do you really think that this amount of PO4 could be used up by plants over 48 hours? It's quite a known fact, that substrate can absorb huge amounts of nutrients. Also up to 60% on nitrigen can be used up (transformed) by bacteria, and escape the tank as N2 gas.


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## Jake101

General question related to this topic. What is the "efficiency coefficient" for nutrient uptake in high light, high co2 situations for plants? Again, surely this is related in several different factors (species, which fert etc.) and is not linear, but if we have fixed co2 and lighting level and we assume that we give just the right amount of ferts for maximal growing in those conditions, how large part of the ferts in water column is used to build the plant mass? Are we generally talking about 90% or 50% or 10%?

 The background for the question is that there usually are many biochemical processes where certain chemical compunds are needed, but they do not directly add plant mass. Also, organisms do not function with 100 % efficacy ever.


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## parotet

ardjuna said:


> By PO4 you can control the growth rate very well. In my test, when I lowered the PO4 dosage to 0.1 mg/L per week, the biomass (live weight) was just around 5 g ... vs. 20 g when I added 3 mg/L PO4. So it's known fact that by limiting PO4 you can slow down the growth rate successfully without making plants suffer.


Ok, that's more or less what I have read in this forum as well in scientific literature regarding wetlands management. But my question is a bit different. Light is the most important driving force in planted tanks, then CO2 (let's say CO2 efficiency, thus including CO2 levels but also dissolution, distribution, etc.) and then nutrients (being PO4 a good controller of growth rate).

The question I was really asking is: in that limiting chain (light > CO2 > nutrients), if high amounts of PO4 are released to the water column and boosting plant growth, can this make my plants hungrier and more demanding regarding CO2? (thus making CO2 manageent in the tank more difficult?). Maybe I'm wrong but if PO4 boosts plant growth it will be also increasing the need of other nutrients uptake (N, K and micros which can be easily unlimited dosing EI, as well as Co2 BUT we all know is not that easy to have really unlimited levels of CO2). Or in other words, assuming that my CO2 is "good enough" for the lights I have: will lower PO4 levels giving me more safety margin for CO2 performance?

Jordi


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## Marcel G

I'm not expert, but as I understand it then plants have some general ratio of nutrient uptake. Light is a driving force of their photosynthesis rate. The nutrients are a building blocks. CO2 is also a nutrient = building block (it's not any different => the only difference is that plants need much more of this nutrient then any other). So look at the picture:





For plants to grow they need a variety of different nutrients, which we can visualize in this example as building blocks (bricks). In order for plant to build _*one leaf,*_ it needs 45 bricks of carbon, 45 bricks of oxygen, 6 bricks of hydrogen, 2 bricks of nitrogen, 1 bricks of potassium, 5 cubes of calcium, 3 cubes of magnesium, 2 cubes of phosphorus, 1 cube of sulfur, and 1 small cube of iron. 




Now imagine that you have in your aquarium (in the water or substrate) the following number of building blocks (= nutrients): 360 bricks of carbon, 2925 bricks of oxygen, 1200 bricks of hydrogen, 40 bricks of nitrogen, 20 bricks of potassium, 10 cubes of calcium, 6 cubes of magnesium, 1 cube of phosphorus, 5 cubes of sulfur, and 3 small cubes of iron. How many leaves can the plant build of this?

The above table shows that plants in our hypothetical example have available in the water (or substrate) as much carbon that would be enough to create 8 leaves, the oxygen amount would suffice for 65 leaves, the amount of hydrogen to 200 leaves, the amount of nitrogen, potassium, calcium and magnesium, both for 20 leaves, the amount of phosphorus for five leaves, the amount of sulfur for 50 leaves, and the amount of iron to 15 leaves. How many leaves can therefore plants create in this environment? According to the law of minimum only 5 ! And this is true even though most of the other nutrients are available in much larger quantities.

On this example you can see that it is absolutely useless to add nutrients to the aquarium indiscriminately. If you would add more nitrogen (N) and potassium (K) into this hypothetical aquarium, it has little efect on the plant growth. Unless you increase the dose of elements which are in the shortest supply, the huge amounts of other nutrients will be absolutely to no good to you (or to plants).

If you add more phosphorus (P) into this aquarium, it ceases to be a limiting factor, and immediately the carbon (C) will become the most limiting factor in our example. Although the growth of plants will increase from 5 building blocks to 8 building blocks, but it will go no further. If you increase the quantity of carbon also (e.g. by adding liquid carbon or pressurized CO2), plant growth will immediately jump to the next level of the most limiting element in a row (which is iron) = 15 building blocks.

In most tanks, I would say that PO4 is the most limiting agent, and all other nutrients are there in much bigger volumes. So if you increase the PO4 level in your tank, your plants will began to grow like mad, because all other nutrients are in a rich supply ... so the real bottleneck will become light (not nutrients). I think if you have 30 mg/L CO2, you'll never be in a situation to limit plants with carbon. Also it's good to know that even plant growth has its limit (around 600-700 µmol PAR).


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## Marcel G

So to answer your question: 





> If high amounts of PO4 are released to the water column and boosting plant growth, can this make my plants hungrier and more demanding regarding CO2?


I would say, "No". If you add more PO4, then the plants will build a little more organic material for their growth. The only power controling their hunger being light.


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## parotet

Ok, understood...



ardjuna said:


> I would say, "No". If you add more PO4, then the plants will build a little more organic material for their growth. The only power controling their hunger being light.


Unless in this high light tank, you add lots of PO4 (EI method is the only one that add 5-10x other systems) and your CO2 is not as good as you thought (not reaching 25 ppm and/or bad distribution)... in that case I guess CO2 would probably become the next limiting agent and a good chance to find problems.

Please correct me if I am doing a faulse assumption but beyond light PAR (which is always the most important driving force and obviously the easier solution to solve potential problems) it looks to me that fertilizing systems with high levels of PO4 require optimum CO2 performance (always in a high light scenario).
Can this fact be the reason why commecial ferts include such low levels of PO4?

Jordi


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## bridgey_c

nice work ardjuna, keep going.

We also know that the law of minimum isnt always true though. Plenty of work has been done on allocation of resources by plants to combat shortages. google will give you the papers.


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## Marcel G

To be honest, I'm not sure if CO2 is needed in such a big amounts. According to my calculations, for plants to grow by 1 g/dm2 per week they would need ~165 mg CO2. In 110L tank (80x35x40cm) the consumption of CO2 by aquatic plants under high light should be 5-9 g CO2 per week. This amount is approx. a daily dosage. In other words, I put 7-times more CO2 into my tank (~35 mg/L), then my plants really need. So if my calculations are correct (or +- correct), then our plants need much less CO2 then we think. And this applies to nutrients also (see my chart).
The word "Rostliny" means "Plants" (my calculated average consumption of nutrients in high-light tank). All units are in mg/L.




So based on this, I would say that optimum/stable CO2 levels are maybe much more of a problem in regard to algae then plants. And the same apply of higher dosages of fertilizer. You all know probably that higher levels of PO4 can eliminate GSA or GDA. The similar apply for NO3 and BGA. So if you have algae problems, then it's maybe better to keep higher nutrient levels, although our plants will never make use of such a big amounts.


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## DivZero

Very interesting discussion!

I am not a plant biologist but would like to add my 2 cents because I studied Life Science and Technology which has alot to do with cells, enzymes etc etc 

I would first like to respond to the above reaction of CO2: CO2 is the carbon source used by plants. And although it is true that you could calculate the dry wait of your plant trimmings to get an estimate of how much CO2 your plants use, it's very difficult to relate this to how much your bubble count should be. This is because you are constantly loosing CO2 which "evaporates" from the surface of your tank. Therefore it's impossible to make an proper "element balance" (unfortunately I don't know the official English term for this) for the carbon element.

I few opinions/thoughts: as stated a couple posts above there is "nutrient" bottleneck. When you look at a plant from cellular level everything comes down to chemical reactions and their reaction speeds. Almost all of these reactions are in one form or another catalysed by enzymes and every enzyme known to men has a maximum reaction speed. This maximum reaction speed is only achieved when all conditions are optimal (pH, temperature, substrate concentration, etc). This substrate concentration (read: nutrient concentration) is where I think it get's interesting. Because concentration dictates whether the maximum reaction speed can be achieved (given all other variables are kept constant i.e. 25C and a pH of 7.0). However, the concentration does not have a direct correlation with the actual turnover from the substrate to a product (i.e. production of a protein which is needed for the plant to grow). For example: for enzyme A the reaction speed is the highest at a concentration of 100 mg/L, consumes 1 mg of substrate and produces 1 mg of product per hour (random numbers). Enzyme B could reach it's highest reaction speed at only 50 mg/L, consumes 2 mg of substrate and produces 2 mg of product per hour. To summarise: concentration of all nutrients could very well play a big role in the growth speed of plants although they don't use all these nutrients. At a lower concentration reaction speeds decrease and thus plants use less nutrients meaning slowing growth.

In addition to my above statement: plants need to absorb nutrients in their cells before they can be used. This absorption often happens either by diffusion or enzymes that transport these nutrients over the cell membrane into the cell. Both these processes run faster at higher concentrations.

Already mentioned is the fact that you can't weight the mass of the roots of the plans. But if you really want to know how much nutrients are used you need to look at the tank as a whole system. The amount of so called biomass, mostly in the form of bacteria in the soil and filter are HUGE. As with any living organism these bacteria also use up nutrients (sources of carbon, nitrogen, phosphor,hydrogen, oxygen and sulfur) and they will use part of the ferts intended for plant growth. This basically means it is very difficult if not impossible to get an accurate estimate of how much nutrients are used based on weekly plant trimmings.

However, there is a easy method of answering the question of how much nutrients you entire aquarium (plants, bacteria, etc) consumes each week (for a given light intensity, making the light the limiting factor). Unfortunately one would need access to a lab... What you need to do is make sure all other nutrients are available in excess. For this you should be fine using recommended EI dosing. After dosing you take a water sample which should be analysed for all added nutrients (except CO2, because it's pointless to measure as it quickly dissipates from the water). Let your tank run for a week and take another water sample. It's important that in the mean time no water changes or fertilisation has taken place (CO2 obviously must be running the whole time as normal). Have the second sample analysed and look at the difference in concentration of nutrients. Now you know EXACTLY how much nutrients you tank uses each week. To make sure your plant growth speed is maximum you need to repeat this experiment with higher concentrations of everything including CO2 (excluding your light). If the result of nutrient uptake are the same, your plants are growing as fast as they can with current lighting conditions, if they increased you are not yet at the max. If they decrease, well... maybe the pH of your tank changed so much due to more CO2 enzymes start to work less efficient.

In a perfectly economical setup you would never do water changes (meaning the concentrations of nutrients remain high) and you weekly add only what has been used. Obviously this isn't possible due to buildup of other chemicals/nutrients in your tank that need to be removed.

So basically I personally think the plants' nutrient uptake is higher at higher concentrations and thus growth speed is higher. Therefore it can be beneficial to have high concentrations of these nutrients present.


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## Crossocheilus

It would seem my random stab in the dark about high concentration is beneficial even for low uptake (makes uptake more efficient) was actually correct or at least partially correct! Slightly off topic but: yay! 

Continue complicated scientific debate...


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## Marcel G

Hi DivZero, this is a really good point!

Also you say that if we want to know how much nutrients are used in our tanks we need to look at the tank as a whole system. As there are other organisms (besides plants) which also use up the nutrients. But I see a difference between what the plants need, and what the whole tank may need. So by weighing the new plant biomass we can find out what plants themselves need. Then using your suggested method we can find out what the whole system needs. And finally, by subtracting these two numbers we can come to know what part of the total amount of nutrients is alloted to plants, and what part to other organisms. So for me it means that we need both approaches to get to some relevant results.

Still, I see a couple of potential problems with your suggested method of finding out the total amount of nutrients needed for the whole system (i.e. measuring the amount of nutrients at the first day, and then at the last day of our test). The problem I see is called "substrate" (and maybe other media like filter). All clay substrates are able to absorb quite a big amount of nutrients from water column (especially phosphates). So how you know that the nutrients were really used up by the microbes? The nutrients could be just absorbed ("stored") without being used up. The next problem is financial, as lab analyses are costly, and we would need to make a lot of analyses to find anything relevant.

So I understand your point, and like it very much. But it means for me, that my task (of finding out the real average consumption of plants in a planted tank with some defined conditions) is probably beyond my financial capabilities. So probably I'll just give up.

One final point to a root biomass. I thought a lot of it, and I would say that its effect on the new biomass gain is not as big. Once the plants create a root system, this root system don't grow too much anymore (maybe except some invasive kind of plants). So even though the roots themselves can make more then 50% of the plant biomass, if you measure the new biomass gain throughout three months, do you really think that root system will grow any further from the day you began your test? I don't think so. Also, during the 3 months period, you trim your plants many times (maybe 10-times). So if you trim your plants in half in each trimming, then you get 5 whole plants in means of biomass (without roots) over this period. But the root biomass stays nearly the same. So I would say that the root biomass will not play so big role (maybe 20%).

Marcel


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## parotet

DivZero said:


> So basically I personally think the plants' nutrient uptake is higher at higher concentrations and thus growth speed is higher. Therefore it can be beneficial to have high concentrations of these nutrients present.


Not sure if you intended to say so but...why it should be beneficial to have high growth speed? As stated high concentrations of nutrients (especially PO4) gives you high growth, but you don't need this super growth (unless you sell plants). The point is to know what plants need.

I agree that the methodology can be probably improved (repetitions is the most interesting part to be included, as stated by the OP). But I don't agree with other aspects mentioned. For example you say it is important to understand the tank as a whole system but this would not give us any useful information regarding plants' needs (it would give us very interesting information for other things, I agree). We all know that part of the nutrients can be stored in the substrate, that microbes may be using some... But I think the point is trying to identify the minimum needs, not to say to folks 'you have to get adjusted to this limit' but again to play with a good safety margin. The interesting part of this thread IMO is to understand how large this safety margin is and (al least to me) if reducing some levels of nutrients (PO4) can indirectly help to reach easily an optimum CO2 performance.

I'm sorry to be a pain each time this issue is discussed (really need to learn more about this and there is plenty of question I still want to understand) but despite all this experiments, methdologies' discussions, etc. there is something quite obvious to me. There are thousands of hobbyist using successfully 'EI approach' but also 'lower nutrients approach'. In both sides we have failures for sure, but also success. EI is not the only method in which you don't use test kits and it is not the only one that gives you this safety margin so many times explained... It is probably the one that gives you MORE safety margin but I'd love to know how much (I recognize that it is probably useless to know how much, lots of people here will say 'don't worry about this, just be sure there is enough') because I want to know if there can be sides effects (sorry again to be a pain, but my concern is about high PO4 and optimum CO2)

Jordi


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## Marcel G

OK, my beloved wife give me an advise how to solve our problem (or at least come closer to its solution).
The obvious solution to this is to set up a tank full of water with an empty filter, put plants into it and use high light. I would attach the plants to some inert stones so that they stay on its place. This way we can know quite precisely how much nutrients the plants will use up in a set time (say one or two weeks). I'll try to do this kind of test. I'll set up an empty tank with empty filtration (to use it just for a water circulation), and after my plants will establish, then I begin my test. I'll put some known (unlimited) amount of nutrients inside this high-light tank and let it analyse in a lab on the first day, second day, third day and last day. I think it is important to analyse the water not only on the first and last day, but also more often in the early days to know if some nutrients degraded (e.g. chelates). What do you think about this kind of experiment?


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## pepedopolous

Hmm, won't there will still be a significant amount of bacteria etc in the 'empty' aquarium (also on the plants) using up nutrients and creating by-products? And they will multiply exponentially until the nutrients run out.

I think it would therefore be better to measure the nutrient use of an aquarium with only hardscape, substrate and a filter and then compare the nutrient usage to an identical set-up but with plants as well.
P


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## parotet

pepedopolous said:


> Hmm, won't there will still be a significant amount of bacteria etc in the 'empty' aquarium (also on the plants) using up nutrients and creating by-products? And they will multiply exponentially until the nutrients run out.


Sure but I guess the system 'plants+microbes' has to go necessarily in the same pack, they do live together in any aquatic ecosystem you create. Therefpre the test would be to know 'the average nutrients uptake by plants and the minimum amount of bacteria needed to support this artificial ecosystem'. Anyway it looks like a good idea to get rid of the substrate which can probably stock part of the nutrients.

Jordi


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## DivZero

ardjuna said:


> OK, my beloved wife give me an advise how to solve our problem (or at least come closer to its solution).
> The obvious solution to this is to set up a tank full of water with an empty filter, put plants into it and use high light. I would attach the plants to some inert stones so that they stay on its place. This way we can know quite precisely how much nutrients the plants will use up in a set time (say one or two weeks). I'll try to do this kind of test. I'll set up an empty tank with empty filtration (to use it just for a water circulation), and after my plants will establish, then I begin my test. I'll put some known (unlimited) amount of nutrients inside this high-light tank and let it analyse in a lab on the first day, second day, third day and last day. I think it is important to analyse the water not only on the first and last day, but also more often in the early days to know if some nutrients degraded (e.g. chelates). What do you think about this kind of experiment?



I think the basis of your experiment is sound. However it is of vital importance your biosystem (read: the tank and all it's content) are as close to equilibrium as possible. This is important because this is also the case in your "real" tanks. Because you have a fixed dosing schedual, fixed water changes amounts, constant lighting and CO2, feeding of fish etc. As a result of this both bacterial and plants growth are more or less the same over time. There growth speeds are always rate limited. The rate limiting factor can be many things, light, nutrients, pH, temperature but also physical limits that dictate maximum speed of enzymes etc. Once a tank and filter is properly cycled, all factors are kept constant, and amount of in this case plant trimming is similar each week a for of equilibrium is achieved. (note: it's important plants are mature and trimmed to keep them constant in size => bigger plants with bigger/more leaves have more surface area to uptake nutrients and a photons for photosynthesis. Once you feel confident the tank is stable and in equilibrium (I.e. looks the same from one week to another, after trimming) the testing can commence!



ardjuna said:


> ...let it analyse in a lab on the first day, second day, third day and last day. I think it is important to analyse the water not only on the first and last day, but also more often in the early days to know if some nutrients degraded (e.g. chelates)



One thing that is excellent from a scientific point of view is taking more than two samples. During my studies we actually had to perform experiments on how to determine at which concentration of a given substrate maximum product formation takes place. This is very important because with this knowledge industrial (bio) processes can be optimised for either speed of product formation and cost reductions. Because now you know at which concentration of a substrate it is just a pure waste to add more, because there is no benefit! But back to the experiment. How are these experiments performed? Without going into too much detail it is quite simple. Because your system is in steady state abd the limiting factor is either lighting, CO2 dosing all other nutrient uptakes are constant en linear over time. So if you take all data from the samples, and plot them against time, you you see straight lines in your plot. However, it is possible that one not the lighting or CO2 are the limiting factor, in which case one of the nutrient concentrations is limiting the growth speed. In this case you would see a decrease of substrate intake over time as the limiting substrate concentration slowly drops, slowing the growth and thus slowing substrate intake further (as substrate intake is dependent on concentration!).

Disclaimer: I do not know if the plants etc take up so much nutrients the data would be significant enough to conclude if the substrate intake is constant or decreasing over time!

If the experiment is performed well this would tell you two things (of this particular tank/bio system!!!): 
1) an absolute nutrient uptake in a week giving a rough estimate of how much nutrients plants actually use. 
2) it might give insights if all nutrients are available to the plants in excess and CO2 and lighting in this particular tank are the limiting growth factors (it can only be one of them btw). If it is shown that nutrients using recommend EI dosing are still limiting the growth speed it shows that that the EI dosing isn't as crazy as it seems

Things this experiment can't proof (with only one dataset): 
1) if nutrients are proven to be in excess we have no idea HOW MUCH these are in excess. It could be as much as 100 mg/L or as little as 1 mg/L. To discover the amount of excess the experiment must be repeated multiple times for each single nutrient until growth speeds decrease. This would probably be a year long study 
2) which factor (light, CO2, which nutrient etc) is the limiting factor in this system will remain unknown.



parotet said:


> Not sure if you intended to say so but...why it should be beneficial to have high growth speed? As stated high concentrations of nutrients (especially PO4) gives you high growth, but you don't need this super growth (unless you sell plants). The point is to know what plants need.



From a biological standpoint plants need very little for their so called maintenance. Little light, little nutrients etc is needed for them to survice. Although I am not an expert on aquarium plants and all the water chemistry I think the important point is the competition aquatic plants have with algae as they need compete bother over light, CO2 and the other nutrients. Therefore I think many of the techniques in high tech aquaria are aimed to battle these algae. One of these techniques is frequent water changes, which removes nutrients (aka byproducts from bacteria such as ammonia) algae can use. It's important tot note that almost every chemical that can be found in the aquarium which is the product of one organism is the substraat thus food for another! And for some reason we only want plants, fish, and denitrifying bacteria (for the most part) in our aquarium and not algae and other organisms . The other "technique" against algae (I think!) are healthy plants that grow. When plants grow they use up nutrients and form biomass (i.e. more plant leaves) which remove these nutrients to be used by other organisms such as algae. One thing I do know is that plants are able to directly use ammonium for their growth, and algae spores need ammonia to germinate (please note that I can't find a reference for this to be true!! after looking most scientific articles state ammonia levels inhibit germination...). This could be also true for other nutrients we don't regularly add, and algae need. With rapid plant growth the plants can lower concentrations of these unknown (to me) nutrients and put a lid on algae growth. 

Also while doing some research for this post I came across this: http://prirodni-akvarium.cz/clanky/Factors Affecting Spore Germination in Algae.pdf
There are many interesting things in this publication with this one standing out in particular:



> The SG (spore gemination) was decreased not only by the lack of nitrogen, phosphorus or magnesium but also when their (and of calcium) concentration exceed certain levels; e.g., nitrate or phosphate at ≥5-fold level, or mag- nesium at 10-fold level of that present in the basal medium inhibited akinete GRM in Westiellopsis prolifica (Agrawal and Sharma 1994a). Magnesium at ≥5-fold level or calcium at ≥2-fold level also inhibited akinete GRM in Stigeoclonium pascheri (Agrawal and Sarma 1982a). *This indicates that SG in algae is sensitive to high levels of inorganic nutrients*. Omission of microelements (ZnSO4, MnCl2, MoO3, CuSO4, Co(NO3)2, H3BO3) from the basal medium increased SG in Stigeoclonium pascheri, and by increasing their concentrat- ion to ≥2-fold levels, the condition was reversed (Agrawal and Sarma 1982a). The presence of microele- ments in the basal medium therefore serves as a check in reaching maximum level of SG under control con- ditions. More study is needed to clear the role of micro- and macronutrients in SG.



This could very well mean that the crazy dosing of EI is having a large impact on germination of many algae species, keeping them in check. In this case the EI dosing would be a nice way to fight algae with plant growth as happy side effect 

Disclaimer: most of the above is either a personal theory and not based on personal experience or scientific research that could OR NOT be applicable to the aquarium ecosystem. Use what I said at own risk and if people think I'm calling out some crazy theories that are wrong, please let me know


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## Marcel G

DivZero said:


> This could very well mean that the crazy dosing of EI is having a large impact on germination of many algae species, keeping them in check. In this case the EI dosing would be a nice way to fight algae with plant growth as happy side effect


This is very good point, DivZero! Because it's quite common experience among aquarist that high concentration of PO4 inhibits GSA (= green spot algae alias genus Chlamydomonas or Chlorococcum). Similar seems to be true with high NO3 concentration and BGA (= blue-green algae alias cyanobacteria). So there can be something on this speculation.


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## DivZero

ardjuna said:


> This is very good point, DivZero! Because it's quite common experience among aquarist that high concentration of PO4 inhibits GSA (= green spot algae alias genus Chlamydomonas or Chlorococcum). Similar seems to be true with high NO3 concentration and BGA (= blue-green algae alias cyanobacteria). So there can be something on this speculation.



Additionally I found an article that states that some (specific) species of cyanobacteria needs very low concentrations of PO4 to germinate, but standard aquarium sources that that BGA (not the species in the article!) need high PO4 to thrive. Maybe I will do some proper research on this topic some time


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## Tim Harrison

I'm not really sure where this is headed and if it's still about answering the questions in the OP. But by its very nature the study lacks scientific rigor...for starters there are far too many confounding factors and you'd need to test the nutrient requirements of every individual species separately with laboratory spec equipment for it to be significantly meaningful...that's a hell of a lot of tests.
However, your study will give you a loose idea of the collective nutrient requirements of the plants in the unique conditions of your tank, and allow you to fine tune your fertz dosing. However as mentioned previously, it is possible to do the same using EI methodology simply by reducing the dosage to the point of negative plant growth response and then notching the fertz back up to the previous dose. This will give you results which are just as meaningful as the ones in your study...


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## Marcel G

Hi Troi,
if you're seeking scientific rigor, then I don't understand your suggestion to "simply reducing the dosage of EI to the point of negative plant growth response". Do you think that this will tell us anything meaningful? How can you be sure what nutrient was missing to cause plants to start exhibit some kind of negative response? How can you be sure that most nutrients don't end up in the substrate? And _*how can you be sure that EI method is based on any reasonable assumptions?*_ You want scientific rigor but at the same time you propose absolutely dilettantish methods. My goal is to find out how much nutrients plants in an average planted tank can need for their growth. I don't need any precise numbers as I know very well that this is impossible to get without years of hard work and lab testing. Still I think we can find out a raw numbers to have at least some idea about the needs of our plants. If I find out the needs of some group of fast-growing aquatic plants under high light (~100 µmol PAR at the substrate) and recommended CO2 levels (~35 mg/L), then I can have a relative certainty that under lower light and not-so-fast-growing plants the demands won't be higher. And even if the plants CAN grow much faster even under lower light if we give them higher dosages of nutrients (e.g. PO4 which can be limiting in most tanks), my goal is to find out some _*reasonable range*_ of nutrients which will _*ensure a good growth *_and vitality of my plants ... as I don't need them to _*grow like crazy *_(as with EI method); I want them to be fit and in a good shape. Why should I try to find out how much nutrients my plants will use up under some absolutely unrealistic conditions like 2000 µmol PAR, 70 mg/L CO2 and unlimited amount of nutrient supply? I'll NEVER have this situation in my tank, nor I want to have it. I don't want for my plants to grow like crazy. I want my plants to grow well (but rather slowly so that I need not to trim them each week).


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## Tim Harrison

Ardjuna, please don't misunderstand me...I'm not seeking scientific rigor...I'm simply pointing out that your study, nice though it is, simply lacks it - and for what it's worth you may as well save yourself the bother of all the hard work because your study will yield comparable results to those achieved using the EI methodology explained above... however with the following major differences...fine tuning EI is simple, and easy.


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## Marcel G

Yes, I understand that, but as I already explained, my goal is different, and your suggested way of fine tuning EI may not lead me to this goal any closer.
I have an experience with my high-tech tank, that when I practice very lean fertilizer dosing, my plants are doing just fine, but the growth rate is much slower. According to my observations the growth rate has much to do with phosphates level. Whether I have 30 mg/L NO3 or just 5 mg/L NO3, the plants grow +- the same if the PO4 level is the same. But when I add more PO4, the plants begin to grow like mad. So it seems that in high-light (CO2) tanks PO4 is probably the bottle-neck. I would like to find out what nutrient levels are needed for good slow growth in average planted tank. Your suggested way of fine tuning EI can be also one way of getting some raw idea, but as with other suggested methods, I'm afraid that it doesn't count with substrate, filter media, bacteria etc. So on one hand I can find out what minimum level is still bearable for my plants, but on the other hand I'll have no idea of how much nutrients ended up in the substrate or filter. Beside this, there can be some shortage of just one or few nutrients which will cause my plants to show some deficiencies, but still other nutrients could be in rich surplus without me having any chance to know that. The main problem with EI is that the nutrient ratio is 30 : 3 : 20 : 0.5 (N : P : K : Fe), but are you sure this ratio is correct? I mean, if you lower the EI dosage (e.g. to 2 mg/L NO3, 0.2 mg/L PO4, 1 mg/L K and 0.03 mg/L Fe per week), and the plants begin to show deficiencies, how you know which nutrient became the limiting factor (bottle-neck)?

Another problem I see with EI metod is that the proponents of this method say very often, that when you get algae, it means the plants are not growing well. This is according to me a complete nonsense. It seems like no one of them is able to admit, that the algae can be related to much more factors then plants alone. Also as already pointed out in some earlier posts, the algae can be suppressed by higher amount of nutrients, so not plants but higher levels of nutrients can be the primary cause of algae suppression in many tanks. I want to say by all this, that when I lower nutrient levels, and get some algae, it may not mean that my plants are not growing well. I may mean that the algae are no more limited by the higher levels of nutrients.


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## Tim Harrison

ardjuna said:


> Your suggested way of fine tuning EI can be also one way of getting some raw idea, but as with other suggested methods, I'm afraid that it doesn't count with substrate, filter media, bacteria etc. So on one hand I can find out what minimum level is still bearable for my plants, but on the other hand I'll have no idea of how much nutrients ended up in the substrate or filter.


Exactly, I couldn't disagree with you less - those are just some confounding factors - that is why either way the results will be equally meaningful/meaningless, so you may as well keep it as simple as possible and use the EI methodology.



ardjuna said:


> Beside this, there can be some shortage of just one or few nutrients which will cause my plants to show some deficiencies, but still other nutrients could be in rich surplus without me having any chance to know that. The main problem with EI is that the nutrient ratio is 30 : 3 : 20 : 0.5 (N : P : K : Fe), but are you sure this ratio is correct? I mean, if you lower the EI dosage (e.g. to 2 mg/L NO3, 0.2 mg/L PO4, 1 mg/L K and 0.03 mg/L Fe per week), and the plants begin to show deficiencies, how you know which nutrient became the limiting factor (bottle-neck)?


The EI ratio of nutrients was just meant to be a rough guide...if you play around with the ratios a nutrient at a time you will still reach your goal but perhaps with less work. 



ardjuna said:


> Another problem I see with EI metod is that the proponents of this method say very often, that when you get algae, it means the plants are not growing well. This is according to me a complete nonsense. It seems like no one of them is able to admit, that the algae can be related to much more factors then plants alone. Also as already pointed out in some earlier posts, the algae can be suppressed by higher amount of nutrients, so not plants but higher levels of nutrients can be the primary cause of algae suppression in many tanks. I want to say by all this, that when I lower nutrient levels, and get some algae, it may not mean that my plants are not growing well. I may mean that the algae are no more limited by the higher levels of nutrients.


I think it's perhaps widely accepted that the presence of algae is due to various factors often interacting synergistically, too much light, high levels of organics, poor plant health etc - and that's not mentioning confounding factors. Accordingly, it would be nigh on impossible to determine with any degree of significance the exact role played by nutrients in any one particular circumstance. Suffice to say EI recognizes this and accounts for it pragmatically in a simple and effective way. But playing around with EI ratios may still give you some idea of what works to help suppress algae within your unique tank conditions...but either way, exactly why will still remain debatable...


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## Marcel G

Thanks Troi for your comments. I have to think of it.


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## Tim Harrison

At the end of the day it's still an enormous amount of work for very little gain...which is why Estimative Index was conceived in the first place and why it remains so popular. It means we can effectively rule out nutrient deficiency and get on with the more difficult problems of optimizing light, CO2, flow, and distribution.


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## Andy Thurston

Isn't darrels duckweed index at the opposite end of the scale. i know is not intended for hightech tanks but surely it could be modified so you can keep nutrients to a minimum in a hightech.


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## Michael W

Big clown said:


> Isn't darrels duckweed index at the opposite end of the scale. i know is not intended for hightech tanks but surely it could be modified so you can keep nutrients to a minimum in a hightech.



This is a possibility. If CO2 flucuation is to blame for the average algae caused in high tech tanks then floating plants could help to test if that is the case, since they have unlimited access to CO2. If the floaters look stressed then one factor could be nutrients and not CO2. This will allow us to get some ideas on what nutrients are lacking over CO2 by dosing different nutrients and see which has the most impact on new growth etc. Granted there are limitations as apparently some floaters won't like the flow provided in high tech tanks or they may suffer from lens burning. But this could well work.

But Troi has my backing on this subject, I don't tend to like to fuss over statistics. I hate over thinking so much. I do not mind reading up on this subject but in practical terms I won't stress over details if needs be.


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## Andy Thurston

Maybe you could use emergent growth instead of floaters as your indicators.
I'm not overly fussed for the numbers either but the idea of keeping more sensitive shrimp/fish in a hightech interests me. I've been talking to a shrimp supplier and i believe its possible with lean dosing and this could be the missing part of the puzzle.
If you play the numbers game then i think you will encounter many problems but if you have a few species of indicator plants i think it would be much easier to manage
Just my thoughts


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## dw1305

Hi all, 
This is an interesting thread. 

As "Big Clown" suggests the "Duckweed Index" is just a simple way of ensuring some plant growth. At least one nutrient will always be limiting plant growth, and usually this will be nitrogen (N), but it could be any of the other macro or micro-nutrients with potassium (K) the next most likely followed by phosphorus (P) etc. 

Ideally I would have liked to quantify the nutrient levels, but it is problematic, particularly for anions like NO3- and PO4---. 





Big clown said:


> Maybe you could use emergent growth instead of floaters as your indicators.I


 You could, it just has to be a plant with access to both atmospheric CO2 and a reasonable amount of light.

I like the "Duckweed Index" because it is a simple, flexible methodology and you don't need to measure anything. If the floating/emergent  plants are green and  growing, don't do anything, if growth or colour declines add NO3- and K+, if the plants don't show a very quick response, it means neither N or K weren't the limiting nutrient, and you can add some Mg++.  

Nitrogen, potassium and magnesium are all mobile within the plant,so you get a rapid response to increased availability. Because non-mobile nutrients would take longer to show a response, rather than going through adding one new nutrient at a time, I just add a complete fertiliser at this point. 

If you wanted to you could straight to the complete fertiliser stage, it really is that easy.

cheers Darrel


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