Weekly nutrient consumption in planted aquarium

[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

 

[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?

 

[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?

 

[Ben C]

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

 

[Marcel G]

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.

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:

 

[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

 

[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.

 

[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

 

[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.

 

[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?

 

[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.

 

[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.

 

[dw1305]

Hi all,

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.

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

 

[Marcel G]

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).

 

[dw1305]

Hi all,

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

 

[Marcel G]

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.

 

[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.

 

[Marcel G]

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

 

[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

 

[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.