# Low Tech CO2 Considerations



## jameson_uk

I have been looking at some potential algae and looking to make sure it does not get any worse.  I have also had some issues with plants not looking great (http://www.ukaps.org/forum/threads/deficiencies.42284).

I know CO2 is going to be limited in a low tech setup and I really don't want to start adding CO2 but wanted to get some background knowledge on CO2 in a low tech tank.   I have read about CO2 being all used up / fluctuating CO2 causing issues.

First off am I right in saying that the pH / KH table is a good ball park as to levels of CO2 in the water?   If my pH / KH are remaining stable then in theory my CO2 levels should be relatively stable?   Also if stable then there is still CO2 in the water available for the plants to use?

Secondly I believe that surface agitation in a low tech setup actually helps keep CO2 levels up as there is more CO2 in air than there is in a low tech tank so I should be looking for reasonable surface agitaton across the whole tank??

Is there anything else I need to consider about CO2 in a low tech setup? (mainly looking to understand the relationships and theory at the moment)


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## ian_m

I assume you are keeping it "low tech" by keeping the lighting levels low. You can also keep ferts low as well.

In that case, varying CO2 levels is not so important as due of low light levels the plants can't make full use of your CO2. Thus running at say 5-15 ppm will be fine.

Water will acquire about 3ppm CO2 from the air regardless of agitation. So if you are adding extra CO2 you need to keep your agitation down or the extra CO2 will simple gas off. You are into the high tech regime of balancing CO2 losses vs CO2 injection.

Maybe consider liquid carbon, rotting fish food, fish poo, compost as an easier method of providing carbon, rather than the possibly unnecessary complications of CO2 gas.

However I would be really interested to see any results.


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## jameson_uk

ian_m said:


> I assume you are keeping it "low tech" by keeping the lighting levels low. You can also keep ferts low as well.


Well I originally started out as just not adding CO2 (pressurised or liquid).   My Juwel Rio 180 has 2 x 45W T5s (0.5W per Litre) so from what I have read the borderline between low and medium light (although the plant deficiency thread says this may be too high).   I am adding some Tropica root tabs (every 6 weeks) and Flourish (once a week) as ferts.



> In that case, varying CO2 levels is not so important as due of low light levels the plants can't make full use of your CO2. Thus running at say 5-15 ppm will be fine.


pH is consistently 7.4 (annoyingly o the border of the low and high range API tests...) and KH has been either 4 or 5.   This I believe this should be 4.8 - 6 ppm which is the low end.



> Maybe consider liquid carbon, rotting fish food, fish poo, compost as an easier method of providing carbon, rather than the possibly unnecessary complications of CO2 gas.
> 
> However I would be really interested to see any results.


If I understand correctly, these add carbon in a form that is not CO2?   
Adding CO2 will drop the pH and potentially if not kept relatively constant this would lead to fluctuating pH (bad for fish) & CO2 (bad for plants, good for algae) ???


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## john dory

I'd remove a t5


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## jameson_uk

john dory said:


> I'd remove a t5


Not sure how easy it will be as it is all a sealed unit that forms part of the hood.  I have read conflicting info as to whether the Juwel units will run with just a single tube (and removing a tube would leave exposed connections.

Either way in terms of CO2 this will make no difference?  Only the plants ability to use it???


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## john dory

You could blank out some of the light.
Maybe wrap tinfoil around a tube,or place something inside the sealed unit.
Maybe fashion an inner lid with something laid over it.


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## jameson_uk

Will look at lights in other thread but in terms of CO2 and theory the other thing I have read about is water changes.

I read something about limiting large water changes in low tech as the CO2 difference between the tank and tap water will lead to fluctuations.

I suspect this is also partly based on having a heavily planted tank where you can't see the substrate but it does raise an interesting point as to whether my weekly 30-35℅ water change is actually not good for the stability of the tank???


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## Daveslaney

Put some floating plants in they will decrease your light intensity?


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## ian_m

jameson_uk said:


> Well I originally started out as just not adding CO2 (pressurised or liquid). My Juwel Rio 180 has 2 x 45W T5s (0.5W per Litre) so from what I have read the borderline between low and medium light (although the plant deficiency thread says this may be too high). I am adding some Tropica root tabs (every 6 weeks) and Flourish (once a week) as ferts.


No. 180l with 90W T5 is definately in the high light region, 0.5W per US Gallon (not litre) is border line between low and medium light.

Your tank is 180l with 90W, thats 47US Gallons with 90W so thats about 2W per US Gallon so definately in high light region. So to keep plants with this light power, you will need to be into CO2, high levels of fertilizer and frequent water changes and all balancing on the algea knife edge 

This is also confirmed from the graph below. Rio 180 is 50cm deep -> 20". So for two tubes at 20" PAR is about 130 which is at the high end of high. PAR will be double if you are using reflectors !!!


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## Tim Harrison

Your lighting is definitely too high, you need to aim for 0.5 watts/gallon, as per ian's advice.
The pH KH thing is a bit of a nonsense in a low-energy tank; CO2 levels are too low.
The water change/fluctuating CO2 level hypothesis is almost certainly hokum, even if it wasn't it shouldn't make any difference in a well balanced tank.
Surface agitation in a low-energy tanks almost certainly helps with greater gas exchange both O2 and CO2. Also in a soil substrate tank the greater O2 levels lead to higher rates of organic matter decomposition and therefore CO2 evolution.

Plant heavily inc floaters, ensure you have adequate flow at least 5x total volume turnover/hr for a low-energy, and if you haven't already consider using a proper soil substrate.
http://www.ukaps.org/forum/threads/the-soil-substrate-or-dirted-planted-tank-a-how-to-guide.18943/


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## jameson_uk

I originally thought I had transposed gallons to litres but I have seen plenty saying 0.5W / Litre being low / medium light.
http://tropica.com/en/guide/make-your-aquarium-a-success/light/
http://www.aquariumgardens.co.uk/lighting-guide-26-w.asp (which appears partly based on the Tropica guide)
http://www.aquatic-eden.com/2006/10/top-3-mistakes-when-starting-planted.html

However I realise that the actual importance here is PAR (which is effectively the level of light actually usable by plants rather than looking at temperature etc. as to how we perceive it ???)
But at £300 I am not going to be getting a PAR meter anytime soon  



ian_m said:


> This is also confirmed from the graph below. Rio 180 is 50cm deep -> 20". So for two tubes at 20" PAR is about 130 which is at the high end of high. PAR will be double if you are using reflectors !!!


If I am reading this correctly you get 130 PAR from the top line being ~65 @ 20" ?   But is that not for high output T5s with a reflector on each bulb? (just based on key more than anything else).   If reflectors double PAR then would this not end up with something 65 PAR and medium light?   I did not think you could determine PAR other than measuring it as the same tube could deliver very different PAR at the same depth in different tanks?    Is this chart averages?   Is it possible that a manufacturer could produce a similar chart for their tubes?

The Juwel lighting setup makes up part of the hood and is an odd size tube (895mm) so changing the lighting would mean changing the hood  which again is going to too costly to do anytime soon.   There are some non Juwel compatible lights but they are all still 45W.   I have read conflicting info as to whether the unit will work with only a single tube in place (and still not sure that even if I could remove one tube how I would actually make the now empty connections watertight).   Perhaps I could swap one of the tubes with a blue moonlight one (here) as although it is still 45W, it has little light in the spectrum that plants can use????

I am still not sure what the actual underlying issue is.   Based on EI dosing it sounds like you cannot really have too much ferts and the whole idea behind this is to overdo it so you always have enough so then the issue becomes the balance of CO2 / Light ??    So assuming I dumped a whole load of ferts in but did nothing about CO2 then the plants would be getting lots of light and ferts but would not be able to do much with them ???  Other the algae which I believe would be thankful for the light and nutrients what happens to the plants?   My lack of understanding makes me think that this would be like the ferts and plants will use what they can and then stop but I am guessing it is far from that simple....    Other than algae what happens if you have lots of light, plenty of nutrients but low CO2 what actually happens (in theory anyway)


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## Manuel Arias

Hi Jameson,

Well, there are a few things that I think are missing in the discussion.

The idea of EI is not far away from what you mentioned: Having enough ferts in water so there is no limited growth coming from lack of these nutrients. This is, in theory, based in the Redfield indexes, but reality is that the method is no longer linked to such indexes. It is just adding more than plants can use, and proportions are not so critical so far you overdose. If nutrients provision overpass the demand, in relation with a certain level of CO2 and light, then no issues are coming from this. The risk of such option is, if you do not manage well light and CO2, then algae can appear, but basically because plants will not be in situation of competing with algae over the available nutrients. The EI method have a corrective step that are the so frequent water changes. This is intended to "reset the system" and avoid an over-accumulation, which creates a potentially advantageous situation for algae if you have not well balanced the other parameters.

Said that, in a low-tech aquarium the issue is no far away of being the same one: If you do not manage light and CO2, in relation to the available nutrients, then you create conditions that favor algae. As in low-tech you actually have less margin to control CO2, accumulation of nutrients in the tank will be a disequilibrium factor, as well as if you do not manage the light well. Why do I say this?

-High light will increase demand of CO2 to cover the photosynthesis rate boost the plants suffer under such good lightning conditions. If this is the case, CO2 dissolved in water will deplete very quick, generating low concentrations of dissolved CO2. Plants are know to face difficulties to absorb CO2 when the concentrations are low, but this is not much the case in algae. Because of that, a high lighting without CO2 injection will allow the algae to use the available CO2 and absorb the nutrients the plants cannot any longer uptake because the limited catabolism caused by the lack of CO2. Hence, algae will appear.

-Low-tech tanks usually are not requiring any or as much a low fertilizing level. However, this does not mean the aquarium is not generating wastes. For instance, a low-tech dense plant will generate lot of dissolved organic matter, which will increase the levels of nitrates in the water column. Combination of high light, plus high nitrates levels plus low CO2 levels is equal to algae. Hence, in my opinion, a low-tech tank needs to change water, too, in order to stabilize the parameters in regular basis. This probably is no needed so frequently as using EI, but at least once a week could be good to avoid the accumulation of remineralized components. Obviously, the strategy must be considered depending on the water parameters (sometimes tap water is just providing high nitrates and/or phosphates).

Apart from that, CO2 concentration in a low-tech tank is very difficult to keep stable, if not impossible. There are a few reasons for that:

a) CO2 diffuses in water at a rate of 10.000 times less faster than in air. This means that uptake of CO2 in low-tech tank heavily planted can be much faster than the diffusion of atmospheric CO2 into the water.
b) CO2 concentration in pure water, when equilibrium with the atmosphere, goes as much as 0.44 ppm. This is extracted straight away of the application of the Henry's constant for CO2 diffusion in water:

Below 5 atm of pressure, Henry's law applies and concentration of CO2 is: [CO2] (mol/l) = 0.032*PCO2. PCO2 is equal to 10^(-3.5) atm, so [CO2] = 10^(-5) M. This, translated to mg/l = 0.44, so *0.44 ppms*. This is the maximum concentration, in pure water, that you can achieve, considering 25 degrees of temperature.

Now, water in aquariums is not pure, which affects to the pH and, hence, to the CO2 concentrations you can reach in equilibrium. More specifically, presence of bicarbonates and carbonates is critical. For instance, a common value of bicarbonates in water is 200 mg/l or 0.2 g/l, which, if no other elements are considered, gives us a pH of 8.2 and a dkH of 18, which once in equilibrium, provides a concentration of dissolved CO2 of 3.4 ppm, what matches with the value provided by Ian (roughly). However, this is only true if kH of water is about 18 dkH. Most planted tanks are kept at different (and usually lower) carbonate hardness levels, which will strongly reduce this amount of dissolved CO2 in equilibrium. For example, the same idea but considering 4 dkH and an equilibrium situation provides 0.47 ppm, so significantly low concentrations of CO2.

This works entirely in a different way when you inject CO2 because you are breaking the assumption of equilibrium in an open system, and also because by doing the injection, you increase the partial pressure of CO2, what allows higher levels of CO2. Due to activity of the plants, the fact the tank is open and the injection of CO2, high-tech tanks never get a real equilibrium unless you dynamically adjust the CO2 injection.

But back to low-tech tanks, top concentration is entirely driven by kH/pH of the solution and an input of CO2 equal to the atmospheric content. Under such situation, CO2 concentrations are rather small and plants are mainly using bicarbonates as input of inorganic carbon, instead of CO2, due to lack of availability. Some plants are not able to do so, so some low-tech tanks will suffer when trying to keep plants not adapted to use bicarbonates instead of dissolved CO2. But in all the cases, a higher carbonate hardness is beneficial in two ways:

a) Increases the bicarbonates concentration, so plants have more availability of this ion.
b) Allow more CO2 in dissolved form being trapped by the water.

This means that kH in low-tech tanks needs to be higher than in high-tech tanks. A good rule of the thumb is trying to preserve kH in about 6-8 dkH, or higher if pH values allow it (but an eye in pH evolution during the day is important).

Additionally, opposite to high-tech tanks, agitation can be a good idea to improve the CO2 levels during the lightning period, as well as granting oxygen to plants and livestock at nights, when plants are not generating O2 but consuming it.

Optimizing the CO2 inputs will then reduce the chances of causing disequilibrium of light/CO2/nutrients levels. The other thing, as already indicated by some, is to reduce the light dose to avoid other problem from that side, and also, as I commented, to put an eye in nitrates levels to avoid a potentially problem of building-up of nutrients.

Unfortunately, it is very difficult to put a number to the amount of light, so you will need to play with all these elements in order to stabilize the tank and avoid the algae. However, as pointed out by Ian, so  far you are adding too much light, so that seems to be a good starting point.

Hope this help.

Cheers,

Manuel


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## jameson_uk

Manuel Arias said:


> For instance, a low-tech dense plant will generate lot of dissolved organic matter, which will increase the levels of nitrates in the water column.


So out of interest (and seen lots of differing views on this) would/could Purigen make things worse?



> Apart from that, CO2 concentration in a low-tech tank is very difficult to keep stable, if not impossible


Would this not affect KH / pH though?  Ie. If CO2 had reduced / been depleted that this would be reflected on measurements?


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## Manuel Arias

jameson_uk said:


> o out of interest (and seen lots of differing views on this) would/could Purigen make things worse?



I have been using Purigen in a few occasions. The stuff is pretty good to get a crystal clear water, and large part of the success into it is associated to its capability to kidnap organic matter in suspension. Seachem also affirms that Purigen absorbs nitrates. I have used it for both things, at different times, and really works. However, the "problem" I see with Purigen is that saturates relatively fast, so its positive effect does not last long. This means that you need to enter in the renovation cycle by using the procedure they mention, which takes practically one day of waiting (but worth doing it to save money). The time you have before saturates it depends on your levels of organic matter and nitrates, obviously. Regarding whether this is good to use or not into a lower-tech tank, the answer is "it depends". For instance, if your levels of nitrates are low, it would have a negative effect, because then it will be removing essential nutrients from water when their level is already low. Besides, degradation of organic matter in the tank also generates CO2 (whenparticles are digested by heterotrophic bacteria and microorganisms). However, if your levels are high, or you have difficulties in keeping them low, then Purigen can be used as emergency treatment to compensate this. On the other side, Purigen electrostatic capability makes me thing that probably have effect also over micro-elements, mainly cations, so perhaps have a down side in such line, especially in a low-tech with no ferts. In summary, I think if a low-tech tank works well, you do not need it. But the product will be of help if you have some specific situations. One of the cases could be the not fully well-known relationship between dissolved organic matter and algae, as it has been observed that high values of DOC are usually a triggering factor for algae. How this happens is not fully understood. ADA recommends some testing to monitor DOC and use that as indicator of algal risk. I think that is a bit an overkill (and besides, no easy testing is available, just one from ADA which is very expensive), especially because in a mature system, nitrates concentration in water will be closely related to DOC, so monitoring NO3 you have a guess of DOC levels and then, times to change water. In this context, Purigen can help, but I think that Purigen would be useful to prevent it, but not to stop it once started.



jameson_uk said:


> Would this not affect KH / pH though? Ie. If CO2 had reduced / been depleted that this would be reflected on measurements?



Yes, it does. In fact, pH cycle in low-tech tank is, curiosly, inverted from the one in high-tech tanks. When you inject CO2, the process is dominant controlling the concentrations of the gas. As a result of that, pH decreases during the time of the CO2 injection. There is no other way to achieve about 30 ppm of CO2, especially at kH levels a high-tech usually have. During nights, as the CO2 injection is not longer applied, pH raises by effect of the degasification process. Plants will add CO2 to water, due to breathing, but the magnitude of that is much smaller than the effect of injection, so degasification process will dominate the pH during the night, and then, raising.

On the other hand, low-tech tanks behave in all the opposite way. During the day, plants will consume the CO2 in water, what increases the pH as result of the removal of protons in the process. During nights, they stop doing so, so levels of CO2 increase and pH reduces.

The changes of pH due to CO2 injection/plant consumption have an effect in the kH, too, and hence, also in the CO2 levels reached at equilibrium point. This is related to the buffer effect of the (bi)carbonates into water and their role in the alkalinity. With pHs over 8.2, certain amount of carbonates is presented in dissolved form. When CO2 is added to water, protons are formed. With presence of dissolved carbonates, part of these protons are absorbed by CO3(2-), forming bicarbonates and avoiding a change of pH in the process. The process of dissolution of CO2 also generate bicarbonates. But CO2 in dissolved form is in chemical equilibrium with the bicarbonates concentration, which means that an increasing concentration of bicarbonates favor the increment of CO2 dissolved into water, just by mere decomposition of bicarbonates into CO2, which further removes protons of water, incrementing the buffer effect. 

In the case of CO2 injection, the process is forced so no equlibrium is reached. The pumping of CO2 into water generates then continously more protons that further consume carbonates, in first place, and with pHs below 8.2 also consumes bicarbonate ions. The removal of these (bi)carbonates causes pH to reduce faster and faster, as less buffer effect takes place. This means that CO2 injection reduces kH in water, unless you had carbonated rocks to compensate the effect. There is not just this chemical process but also the active consumption of bicarbonates by the plants, which also reduces the kH value.

In the case of low-tech tanks, the absorption of bicarbonates by the plants takes also place (in fact, as mentioned, it is the main way for most aquatic plants under low CO2 conditions), and there will be also a chemical consumption, by buffer effect, at nights, when CO2 increase due to lack of CO2 consumption and increment of concentrations due to breathing. In aquariums with a few plants, the effect will be not much noticeable, especially if the water changes are regular and the kH is "renovated" somehow at this moment. But in a low-tech with a dense vegetation, the effect can be significant, and in fact, a factor to consider, as if kH drops too much, we can favor appearance of algae and difficulties in the plants to grow.

In my opinion, monitoring kH in low-tech tanks is especially important. As it is a key factor to supply of inorganic carbon to the plants, controlling the kH inside the tank and in tap water can be rather important. Tap water can also have varying kH values. Especially during summer, evaporation of the reservoirs can increase the values of kH, so it is something to consider.

Hope this answer your question.

Cheers,

Manuel


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## ian_m

Manuel Arias said:


> Seachem also affirms that Purigen absorbs nitrates.


No it doesn't, which is why you can use it in a planted tank dosing nitrates. What it does remove is nirtogenous organics which when decomposed by bacteria produce nitrates, so thus does, to a certain extent, control nitrate levels in your tank.


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## Manuel Arias

ian_m said:


> No it doesn't, which is why you can use it in a planted tank dosing nitrates. What it does remove is nirtogenous organics which when decomposed by bacteria produce nitrates, so thus does, to a certain extent, control nitrate levels in your tank.



Well spotted Ian, you are right. It is Prime the product who actually makes "deactivate" the nitrates. But in the application, result will be the same: If removes the source of nitrogenous components and the plants uptake nitrates, you will observe a reduction, anyway. Thanks for the correction.


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## Daveslaney

Nice info,Thank you.
So i am i right in thinking the only water parm in your tank water is the KH and this only effects the waters abitity to absorbe the CO2 evrything else is irrelevant? From messuring co2 levels point of view?
The PH is relevant to an extent i suppose. But it is the 4dkh water in the drop checkers ph that makes the coulour change and gives us the 30 ppm levels for the co2. Regardless of the tank waters ph as they are both independant due to the airspace in the dropchecker.


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## Manuel Arias

Daveslaney said:


> Nice info,Thank you.
> So i am i right in thinking the only water parm in your tank water is the KH and this only effects the waters abitity to absorbe the CO2 evrything else is irrelevant? From messuring co2 levels point of view?
> The PH is relevant to an extent i suppose. But it is the 4dkh water in the drop checkers ph that makes the coulour change and gives us the 30 ppm levels for the co2. Regardless of the tank waters ph as they are both independant due to the airspace in the dropchecker.



You are welcome! Glad to help.

About your comments:

-kH is relevant for CO2 concentrations, both in high-tech and low-tech. However, as in high-tech you inject CO2, kH has less weight, as it will impact more in terms of stability, CO2 optimization and times. Nonetheless, many aquatic plants appreciate having some bicarbonates in water to use, so it is also good idea trying to have a reasonable kH. In low-tech tanks, kH is the only way to control CO2 at some extend, or better said, to improve the CO2 levels. That, and a good aeration/agitation strategies to maximize CO2 diffusion from atmosphere to the water.

-pH is relevant because it plays a role in the form in which the dissolved CO2 is present. For instance, with pH above 8.2, there is no CO2 in form of dissolved gas and all the CO2 is in the form of bicarbonates. Even if plants appreciate bicarbonates, most of them prefer to use CO2 because it requires no investment of energy to absorb it, making more efficient, in terms of energy, the full photosynthetic chain. With pHs below 8.2, a fraction of the inorganic carbon is present in form of CO2 dissolved gas. This fraction increments with the reduction of pH, so the lower the pH, the larger the fraction. With pHs below 5.5 or so, all the inorganic carbon in water is in form of dissolved gas. However, one thing is the proportion between species (CO2, HCO3, CO3) and another the total amount. Very low kHs will alow very low pHs, but then the maximum values of CO2 you can get are much lower, under the low-tech approach.

-Regarding the drop checker, you are right also, at some extend. The drop checker is isolated from the tank for good reasons, and one is to ensure that parameters of the indicator solution are kept inside the expected values. For instance, change of colour in the drop checker is just due to changes in the pH of the solution. In other words, drop checker is really a pH meter. The thing is that there is a connection between pH value and CO2 concentration, whenever the kH value is also known. In the drop checker, the combination of 4 dkH plus a pH of about 6.8-6.7 gives you a value of CO2 concentration of about 30 ppm, and this corresponds with the lime green colour of the indicator solution. So, essentially, in the drop checker, it is assumed (and usually is correct) that only reason of changes of pH are associated to changes in the CO2 concentrations, which then causes the changes of colour.

For low-tech tanks, drop checker can be interesting, but probably of not much use, due mainly the CO2 levels are so low that indicator solution will stay around bluish colors all the time. It is much better, in these cases, to take measurements of both pH and kH to estimate the current CO2 concentrations.

An interesting and thorough, but technical, article about use and principia of drop checkers is found here: http://www.thelivingtank.co.uk/2016/07/article-co2-drop-checker-ultimate-guide.html

Hope this help.

Cheers,

Manuel


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## jameson_uk

A lot to take in  

So is the main issue algae?  Is it that given the right conditions algae can actually deprive plants of what they need rather than just the excess (which the plants cannot use due to a light  / co2 / nutrient imbalance) causing algae?

Ie. Is providing the conditions for algae detrimental to the plants?


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## Manuel Arias

Hi again Jameson,

Not exactly. Algae are what is called opportunistic organisms. Opportunism is not something specific of a given animal, plant, bacteria, fungi or whatever living group you consider, as it is an adaptative strategy to survive. Opportunistic organisms take advantage of any environmental condition they could exploit, basing its capability of survival into their plasticity in order to "feed" from unexpected sources whenever they are present. Algae are not just taking any excess of nutrients. They are taking what the plants cannot because they are simpler organisms which gives them the possibility of "working" with less food than plants. In an easier example, think in plants as human beings, and algae as ants. A human being cannot survive merely by eating a few crumbles in the floor of the kitchen, but ants can feast in them. However, if there is a full bread loaf, the humans can eat everything and not leaving remainings for the ants, which then cannot thrive in the house. 

The situation with algae and plants is similar. Algae cannot thrive when the conditions are right for plants because the plants are making use of all the available resources, at a time scale that is minor than the accumulation of nutrients. However, when plants suffer of nutrients/light/CO2 limitation, then algae can take advantage of it, growing at shorter time scales.

Besides this effect, many organisms try to adapt the environment to their needs. When algae appear, they start to affect to the normal cycle of the tank, so the problem, if not tacked, gets worse and worse. For instance, they start to grow over the plants, shadowing them and/or reducing water circulation around them, which empowers still more the algae growth. This is the reason why tackling algae as soon as they start to appear is so important.

Hope this is more clear now. 

Cheers,
Manuel


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## hitmanx

Sorry to drudge up this old thread, but the info here is very interesting and comprehensive...

But I have a question along these lines regarding buffering substrates and how they effect kh in the low tech system... given that my aquasoil and clay substrate is meant to buffer, I do not add any bicarbonate to my change water, instead using only gh remineralised RO... my kh values are very low... usually no more than 1 or less... 

Can I assume that the potential co2 concentration in my tank is severely limited because of the low kh values or does a buffering substrate effect this differently? 

My shallow wide tank has a lot of surface aggitation... the coast to coast overflow and HOB planter boxes that spill water into it further the aggitation and the unsealed shallow wide sump also presents a lot of surface area for co2 gas exhange... 

But I am seeing what looks like co2 related deficiencies in most of the fast growers despite a valiant attempt at good flow and distribution of the limited co2 I have... as Clive has said many times, look there first especially with holes and deterioration in leaves, but the low tech system needs to be taken into consideration...

I am not seeing algae much at all yet, but deficiencies are the first step to disaster...


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## dw1305

Hi all, 





hitmanx said:


> Can I assume that the potential co2 concentration in my tank is severely limited because of the low kh values or does a buffering substrate effect this differently?


Whatever the dKH is it doesn't effect the amount of Dissolved Inorganic Carbon (DIC) in the tank, that is set by the CO2 ~ HCO3- ~ pH equilibrium and relates to the 400ppm CO2 in the atmosphere. 

All that changes is <"the form the DIC is in"> (dependent upon pH). 

cheers Darrel


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## Oldguy

hitmanx said:


> remineralised RO



Is it possible to check the water in the tank. CO2 will only dissolve in water to a limited extent no matter how well the water is agitated an equilibrium is reached. If your tank water is very low TDS then plants will struggle to grow. Without bicarbonates you plants might be extracting dissolved free CO2 faster than it can dissolve back into the water. With bicarbonates most plants can extract CO2 from the bicarbonate ions and form carbonate ions which will cause the pH to rise. This is usually countered with weekly large water changes. Have you considered mixing straight RO water with tap water to give a total hardness of say 50 ppm (soft water) or more tap water to give a harder water. Or use rain water and tap water to the same effect but at less cost. Tap water also contains nitrates, phosphates and some iron, all of which are needed for plant growth.

Low cost TDS and pH pen type meters can be obtained from ebay and could be of use. However, both will give unreliable results with water with a very low mineral content ie RO water and rain water. But comparisons between tank and tap water could be informative. Your water supply company should publish the water analysis for your tap water.


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## hitmanx

Oldguy said:


> Is it possible to check the water in the tank.



When filled in 2017 the water was 50/50 tap and RO so the gh and kh was about 12dgh/12dkh... that year I did only top ups with store bought RO, with no water changes... 

In 2018 I started using homemade RO and 5 to 10% weekly water changes with salty shrimp remineralised RO to about 6dgh or 200ppm... the tank has hovered around 300-400ppm using my tds pen... 

Last I looked ph was 7, gh was 10 and kh was 1 and tds was 295...

I will taking some measurements again at different times of the day to glean some hard numbers...


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## Oldguy

hitmanx said:


> Last I looked ph was 7, gh was 10 and kh was 1 and tds was 295



TDS does not appear to be a problem. It could be that your plants are removing CO2 faster than it can be absorbed from the atmosphere. CO2 is soluble in water compared to other gases but it is only slowly absorbed. All your plant growth: sugars, starches and cellulose came from the CO2 dissolved in the tank water.

Will be interesting when you have more data. Unfortunately I know nothing about 'salty shrimp'.

If you had good plant growth when the tank was first set up you could consider going back to 50:50 RO/Tap water but with much larger weekly water changes. What are your micro nutrients like. I ran low tech for years but always added chelated iron and additional potassium. I found obligate aquatics did OK with 10% water changes but emergent plants grown submerged started to become brittle and fall apart. However when 'rested' and grown in soil in a damp atmosphere, cutting became good to go for the next year. I think this was all down to CO2.


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## micheljq

I tend to disagree with something here.  For some people low tech = low light, and i tend to disagree with that.  Although it is clearly quite difficult to keep a medium/high light tank without co2 injection, i have seen over the years on the internet plenty of examples of people who were successfull doing this.

As for myself have kept what i think is a medium lit tank without co2 injection for 14 months, without major issues and with minimal effort.  You have to be careful what species of plants you keep and you must limit the number of different species in the tank, because they compete each other for the limited co2.  It is difficult, but difficult does not mean impossible.

Michel.


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## dw1305

Hi all,





micheljq said:


> As for myself have kept what i think is a medium lit tank without co2 injection for 14 months, without major issues and with minimal effort.


I also use what ever light I have to hand as well. I just have a <"greater mass of plants if I have more light">, I don't do anything different.

cheers Darrel


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