Does excess co2 inhibit plant growth?

jaypeecee

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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
 

dw1305

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Hi all,
.......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
 

dw1305

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Hi all,
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.
oxygen-solubility-water-png.png

cheers Darrel
 

jaypeecee

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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
 

dw1305

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Hi all,
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.
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
 

jaypeecee

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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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"Excess" CO2 can inhibit plant growth but it does so indirectly. If the water is poorly buffered, and there are materials that are high in heavy metals, the very low pH can cause these metals to release in excess and can cause toxicity in many plants.
 

Alex C

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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!
 

dw1305

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Hi all,
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
 

jaypeecee

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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
 

jaypeecee

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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
 

Witcher

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

Bryce

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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.
 

jaypeecee

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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
 

jaypeecee

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@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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