# Does excess co2 inhibit plant growth?



## Kezzab (5 Mar 2020)

Hi, in my Sunday Scape journal it has been suggested that very high co2 injection could inhibit plant growth and encourage algae because it may have a detrimental effect of the tank's benefical bacteria due to creating very low ph.

Wondered whether there were any more thpughts on this?

For info its a 15l tank. Drop checker is yellow verging on clear. Water is very soft, TDS 30ish. Remineralised with pinch of TNC GH Boost and adding 1ml TNC Complete 1ml to take TDS to about 120ish. Wc is 50% daily at moment. I dont have any means of measuring ph right now.

I'm having persistent problems with soft green smothering thread like algae plus a bit of BBA and staghorn here and there.

Tank has no livestock.

Any insights?


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## Dr Mike Oxgreen (5 Mar 2020)

What’s your light?


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## Kezzab (5 Mar 2020)

2x aquael leddy, 7hrs.

Ive had same set up in previous recent scapes with no issues...


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## Kezzab (5 Mar 2020)




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## Bryce (5 Mar 2020)

Does excess co2 inhibit plant growth?  No . However there is a point of diminishing returns, and that point is extremely hard to get to. Just because that same lighting worked for one tank doesn’t mean it will for another. Your algae issues are not enough co2 for the amount of light your using. Back off the light, keep co2 cranked, and keep a good fertilized water column, with good flow and things will turn around. As always a clean filter and tank is always important.


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## Kezzab (5 Mar 2020)

Mmm, problem was worse with half the light...


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## Bryce (5 Mar 2020)

Look at the ferts if you feel the light is right. I’m not familiar with the one you’re using. Is it based on EI? I personally use heavy Co2, EI ferts, and low to low med light. I looked at your journal. No , the bacteria in your tank does nothing for algae, it does not keep it away.  That’s was probably said with good intentions, but sorry flat out false. It simply breaks down waste , as I am sure you understand the cycle.


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## Kezzab (5 Mar 2020)

Hi, its a complete fert, 3x recommended dose is EI equivalent and thats what im dosing.

The bacteria theory is, i think, that the high co2 leads to the tank being sort of perpetually uncycled and unstable. I can see some possible sense in that. But it seems a stretch.
K


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## Bryce (5 Mar 2020)

Kezzab said:


> Hi, its a complete fert, 3x recommended dose is EI equivalent and thats what im dosing.
> 
> The bacteria theory is, i think, that the high co2 leads to the tank being sort of perpetually uncycled and unstable. I can see some possible sense in that. But it seems a stretch.
> K


   I don’t know , your co2 level would have to astronomical . I see what your saying. I never herd of somebody co2 so high it destroys the bacteria. Even in huge body’s of water the co2 level is greater then we could ever achieve in a tank and the cycle is perfect.


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## CooKieS (6 Mar 2020)

How is the flow in your tank?


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## Tankless (6 Mar 2020)

What are the signs of determining adequate flow?


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## Kezzab (7 Mar 2020)

Flow is good. Spray bar, can cleary see circulation through the whole tank.
K


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## alto (7 Mar 2020)

I don’t know about some of the conclusions being bandied about (how often do I get to use that phrase  )
but I’m fairly certain that natural habitats with very low pH eg, 3-4 often have low plant mass - though this may just be circumstantial 
(and my recollections may be wrong    )

But a lot of water based systems (including inside plant cells) like that “physiological pH” so if plants are expending biochemical energy maintaining cellular pH (or I’m leaping about to my own conclusions here ) then plant growth will be depressed 

I guess what I’m really wondering is 
Why such high CO2  that the drop checker (which is a pH indicator solution) reads clear?

I can imagine that MC mat FAIL triggering considerable imbalance, in a system that was already having issues 

I also read the bacteria comment as being more general re the complex “normal flora” that develops in aquatic systems 
(and this goes back to those same low pH natural waters which are reported to have low levels of measurable bacteria)

Anyway I’m just rambling


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## Kezzab (7 Mar 2020)

Hi @alto, helpful response 

Co2 is so high because there is no livestock so my assumption was it would help. In practice its only 1.5bps and 600grm bottle lasts 6 months coz the tank has about10ltrs water.

I think i agree thst the mc mat failing was a bigger problem, but i removrd all the rotting material and while this seems to addressed the development of bba and staghorn on the plants the fuzzy green thread stuff is still a problem.in most of the carpet.

Im currently hoping that the patches of healthy mc growth will eventually smother the stuff thats covered in algae and itll sort itself out.

I may get a ph pen just out of curiosity to see if the ph does get that low..

K


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## Barbara Turner (7 Mar 2020)

What happens at night? Do you get a massive colour change. 
I would do a pH profile ASAP and aim for a 1 pH drop. 
Big PH swings could be giving you issues. 

Other common problem is flow rate. 
Have you measured your pump flow rate?  I currently run over 10x and it makes a massive difference to transporting the nutrients and co2 around the tank.  
I'm sure there will be plants and algae that prefer the more acidic water, some plants and algae won't do so well.


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## Zeus. (7 Mar 2020)

Kezzab said:


> co2 injection could inhibit plant growth



No it will boost growth - Plants in DSM thrive with 400ppm CO2, [CO2] is the limiting factor in our tanks most of the time hence we inject it. 



Kezzab said:


> very high co2 injection encourage algae because it may have a detrimental effect of the tank's benefical bacteria due to creating very low ph.



well your waters pH also depends on your waters dH (Hardness) to start with so tricky to anwser in a way, however with the amount of CO2 we inject I dont see it as an issue, if your using RO water neat or have very soft water and not remineralsing it then yes it could be an issue as controlling pH is very hard with RO/very soft water but it would affect the tanks inmates well before the bacteria

Check your tap water here for report


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## Barbara Turner (8 Mar 2020)

Zeus. said:


> would affect the tanks inmates well before the bacteria





Kezzab said:


> Tank has no livestock.


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## foxfish (8 Mar 2020)

I think there is a limit as to how much C02 water can hold but I can’t find an answer on the internet?
I seem to remember it being suggested that it was near impossible to get over 50ppm ?


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## dw1305 (8 Mar 2020)

Hi all, 





foxfish said:


> I think there is a limit as to how much C02 water can hold but I can’t find an answer on the internet?


It is a very soluble gas, so you can dissolve a huge amount in cold water. Looking at the graph you can get a theoretical maximum value of about 1500 ppm at tank temperatures and atmospheric pressure. Chart from  the <"solubility of gases in water">.





foxfish said:


> I seem to remember it being suggested that it was near impossible to get over 50ppm ?


I guess that is because the more CO2 you dissolve in the water the steeper the concentration gradient is between the water and the atmosphere, and the quicker it escapes. Because there is only ~ 400ppm of CO2 in the air, that gives you an equilibrium value of less than 1 ppm dissolved CO2, via Henry's law.  

*I don't know how much dissolved CO2 there is in a can of coke, but <"my guess is quite a lot"> scrub that, it is an incredible amount . I've just found that coke link, which says "_0.14mol CO2 in 1000mL_".

The RAM of carbon (C) is 12 and of oxygen (O) = 16, and we have two of them so that is 32 and the RMM of CO2 is 12+32 = 44, 44 x 0.14 is 6.16g and mg/L is equivalent to ppm. So you have about 6160 ppm of CO2 in the can, although 0.15% (about 0.01g) of this will be dissolved carbonic acid (H2CO2) and some of the gaseous CO2 will be in the headspace of the can above the liquid. 

cheers Darrel


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## foxfish (8 Mar 2020)

I am sure Tom Barr wrote about this but I have searched for an hour without finding it.
I am certainly “not” sure about anything relating to this subject however it just sticks in my mind he wrote about 50ppm being a limiting factor .
Perhaps that was based on normal planted tank perimeters such as surface movement or flow rates or something else?


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## Alex C (8 Mar 2020)

Is the 50ppm 'limit' something to do with the maximum amounts fish can cope with?


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## jaypeecee (8 Mar 2020)

Alex C said:


> Is the 50ppm 'limit' something to do with the maximum amounts fish can cope with?



Hi @Alex C 

I have found it difficult to get a definitive safe limit for CO2 toxicity to freshwater aquarium fish. The best I've been able to find was something I discovered recently related to Rainbow Trout. This is the reference below and note it's only an abstract but it contains useful information nevertheless. Here it is:

https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1365-2761.1979.tb00170.x

Take a look at the date of this paper. This research was carried out no less than forty years ago!

JPC


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## dw1305 (8 Mar 2020)

Hi all, 





jaypeecee said:


> .......I have found it difficult to get a definitive safe limit for CO2 toxicity to freshwater aquarium fish. The best I've been able to find was something I discovered recently related to Rainbow Trout. This is the reference below and note it's only an abstract but it contains useful information nevertheless. Here it is:
> 
> https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1365-2761.1979.tb00170.x
> 
> Take a look at the date of this paper. This research was carried out no less than forty years ago!


This subject has come <"up a few times on the forum">, but because you can't search for "CO2", you have to search for terms like <"hypercapnia"> and  <"Bohr Root"> effect.

I'm not a CO2 user, so I don't have any practical experience of keeping fish at enhanced CO2 levels. It isn't an avenue I'm ever likely to go down, but if I were I would be aiming for a lot less than 30 ppm CO2.

cheers Darrel


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## dw1305 (9 Mar 2020)

Hi all, 





dw1305 said:


> I've just found that coke link, which says "_0.14mol CO2 in 1000mL_".


I've also found the graph (that I couldn't find the other day) <"showing the effects of pressure"> on gas (in this case O2) solubility.

I would assume that CO2 shows a similar response to increasing barometric pressure. 



 
cheers Darrel


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## dw1305 (9 Mar 2020)

Hi all, 
Here is the actual one for CO2.



 
cheers Darrel


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## jaypeecee (9 Mar 2020)

dw1305 said:


> I'm not a CO2 user, so I don't have any practical experience of keeping fish at enhanced CO2 levels. It isn't an avenue I'm ever likely to go down, but if I were I would be aiming for a lot less than 30 ppm CO2.



Hi Darrel,

So if we were to set an upper limit of, say 20 ppm CO2, which fish species would be suitable in this environment? Which Fish Order/Family/Group should we consider? Clearly, plecos are not candidates.

JPC


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## dw1305 (9 Mar 2020)

Hi all, 





jaypeecee said:


> So if we were to set an upper limit of, say 20 ppm CO2, which fish species would be suitable in this environment?


Just keep away from fish from cool, flowing water really. So definitely not Hillstream Loaches. 





jaypeecee said:


> Clearly, plecos are not candidates.


Bit of a funny one really, fish like _Pterygoplichthys gibbiceps _are very tolerant of low oxygen levels and can take in oxygen from gulped air, against that some of the rheophilic _Chaetosoma_ spp. require really high oxygen levels. Air gulping is an ancestral trait in both _Corydoras _and Loricariids, derived from their mutual ancestor.  

Labyrinth fish should all be all right, and if I wasn't sure, fish from acid black-water conditions are more likely to be tolerant of low oxygen than those from alkaline conditions, although there maybe other reasons why they are difficult to keep. 

cheers Darrel


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## jaypeecee (9 Mar 2020)

Hi Darrel,

I'm a tad confused.

I was talking about CO2 but you are talking about fish that are tolerant of low O2 levels. Am I missing a trick?

JPC


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## Alex C (9 Mar 2020)

Correct me if I'm wrong but I guess the reason for talking about low O2 tolerance is not necessarily that there will be less O2 in the water with more CO2 but that the O2 will be 'harder' to get given the change in concentration.

So while you're increasing CO2 you're not looking for fish that can cope with CO2 but rather a fish that can handle an environment where the O2 is harder to get.

Imagine a ball pit full of red and blue balls, if you keep adding red the blue don't leave the pit but it becomes harder to get a blue ball out, if that makes sense.

Caveat the above with, just my thought on why, not a definite truth!


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## dw1305 (9 Mar 2020)

Hi all, 





jaypeecee said:


> I was talking about CO2 but you are talking about fish that are tolerant of low O2 levels. Am I missing a trick?


It is exactly as @Alex C says, they are directly related because the haemoglobin transports both CO2 and O2.

There is a full description in the <"fish respiration"> link earlier in the thread. The issue is that at the gills, the diffusion of gases depends upon the concentration gradient between dissolved gases in the water and dissolved gases in the blood. If you have high CO2 levels in the water more haemoglobin molecules will be unavailable to pick up an oxygen molecule. 

Fish that are most vulnerable to low oxygen and/or high CO2 are those with a strong <"Bohr"> and <"Root"> effect. Fish that are capable of <"surviving low oxygen levels"> have a weak Bohr effect and no Root effect (Carp _Cyprinus carpio _is the given example).

cheers Darrel


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## jaypeecee (9 Mar 2020)

Hi Darrel

This is b-e-g-i-n-n-i-n-g to make a lot of sense. Will re-visit tomorrow when my brain is hopefully working again!

JPC


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## jaypeecee (10 Mar 2020)

I now feel like Archimedes when he got out of that bath and shouted 'Eureka'! What you, @Alex C and @dw1305  were saying just didn't sink in - last night. One of those 'the lights were on but there was no-one at home' situations. Anyway, I'm with you now. I love that 'red and blue ball' analogy - excellent!

I'll now read the fish respiration link.

JPC


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## Witcher (10 Mar 2020)

Assuming that high amount of CO2 will make one of other nutrients quickly depleted, we can say that excess CO2 may inhibit plant growth.


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## Bryce (10 Mar 2020)

Witcher said:


> Assuming that high amount of CO2 will make one of other nutrients quickly depleted, we can say that excess CO2 may inhibit plant growth.


That’s correct,.....but at that point you have a nutrient deficiency. Or you could say I have extremely high co2, very high ferts but your lights are too weak, now you have a lighting deficiency. It’s a circle, everything needs balanced. But to answer the question, no high Co2 doesn’t inhibit plants growth. I believe I mentioned this before but there is a point of diminishing returns.


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## dw1305 (10 Mar 2020)

Hi all,





jaypeecee said:


> Anyway, I'm with you now. I love that 'red and blue ball' analogy - excellent!


That was a good one, and definitely better than I could manage. 

cheers Darrel


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## jaypeecee (10 Mar 2020)

Hi @Kezzab 

I apologize for unintentionally steering this thread away from your original question. Unfortunately, this does happen. Hope you feel that you got answers to your original question.

JPC


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## dw1305 (10 Mar 2020)

Hi all, 
@jaypeecee you might be interested in what Tom Barr (@plantbrain) siad in 2011. In <"Oxygen in a planted tank">. 

cheers Darrel


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## jaypeecee (10 Mar 2020)

dw1305 said:


> @jaypeecee you might be interested in what Tom Barr (@plantbrain) siad in 2011. In <"Oxygen in a planted tank">.



Hi Darrel,

Thanks for the link. That's a useful post by Tom Barr. *Take-home message*: when talking about CO2 toxicity to fish, always include the O2 concentration. In other words, quote the [CO2]:[O2] ratio or vice versa. Whenever I've done spot checks, the [CO2]:[O2] ratio varies from 1:2 (early morning) to 4:1 (early evening). I don't have the luxury of datalogging CO2 and O2 probes. Instead, the tests are done manually using a JBL O2 Test Kit and my DIY electronic version of the humble drop-checker. The O2 concentration rarely drops from 8 ppm. I've only ever seen lower figures with the JBL test kit when measuring the O2 concentration of the water in Daphnia culture containers.

JPC


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