# How Much CO2 Do Fish Produce?



## jaypeecee (1 Feb 2019)

Hi Everyone,

OK, I realize that my question is not easy to answer and I'm not looking for a definitive reply. But, does anyone have _any_ idea how much CO2 fish produce - either by excretion from the gills, urine or faeces? Indeed, which of these three would account for most of the CO2 produced by fish? I am assuming it would be mostly from the gills but I would welcome any replies. Is the amount of CO2 from the fish a significant source for live plants?

JPC


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## micheljq (1 Feb 2019)

Hello, from what i have read on many sites, something like 0,6ppm not even 1ppm.

Michel.


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## Tim Harrison (1 Feb 2019)

Co2 from fish respiration, on its own, is not really significant enough to contribute anything meaningful to plant growth. The graph below is from Diana Walstad's book and can be found in Updating Ecology of the Planted Aquarium. It gives you some idea of CO2 levels in an aquarium and how they change during the photoperiod.
In a soil substrate tank the CO2 released through the decomposition of the organic matter is perhaps a more significant source for plant growth, but as you can see from the graph below it soon becomes depleted during the photoperiod.
To compensate Diana advocates the siesta period during which the lights are turned off and photosynthesis ceases, this in turn allows CO2 levels to recover (the dotted line), but that is still a somewhat contentious issue.
I think many if us consider a stable CO2 conc to be more conducive to healthy plant growth, even if it means the conc is lower, and in a low-energy tank this is best achieved by ensuring good surface agitation and gas exchange. It also helps to increase O2 saturation which in turn increases aerobic decomposition and CO2 evolution. This technique works best in tanks with a large surface area to volume ratio; shallow tanks.
It's not apparent in the graph below since Diana was of the opinion that surface agitation wasn't desirable, since it off gassed CO2. She has since revised her opinion.


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## jaypeecee (1 Feb 2019)

Tim Harrison said:


> Co2 from fish respiration, on its own, is not really significant enough to contribute anything meaningful to plant growth. The graph below is from Diana Walstad's book and can be found in Updating Ecology of the Planted Aquarium. It gives you some idea of CO2 levels in an aquarium and how they change during the photoperiod.
> In a soil substrate tank the CO2 released through the decomposition of the organic matter is perhaps a more significant source for plant growth, but as you can see from the graph below it soon becomes depleted during the photoperiod.
> To compensate Diana advocates the siesta period during which the lights are turn off and photosynthesis ceases, this in turn allows CO2 levels to recover (the dotted line), but that is still a somewhat contentious issue.
> I think many if us consider a stable CO2 conc to be more conducive to healthy plant growth, even if it means the conc is lower, and in a low-energy tank this is best achieved by ensuring good surface agitation and gas exchange. It also helps to increase O2 saturation which in turn increases aerobic decomposition and CO2 evolution. This technique works best in tanks with a large surface area to volume ratio; shallow tanks.
> It's not apparent in the graph below since Diana was of the opinion that surface agitation wasn't desirable, since it off gassed CO2. She has since revised her opinion.



Hi Tim,

Thanks for the reply. I see what you mean - after just over two hours, CO2 is down to 4ppm. Not exactly conducive to plant growth! So, it's almost irrelevant what proportion of this figure is produced by the fish.

JPC


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## jaypeecee (1 Feb 2019)

micheljq said:


> Hello, from what i have read on many sites, something like 0,6ppm not even 1ppm.
> 
> Michel.



Bonjour Michel,

Thanks for your reply.

Along with Tim's reply, you have confirmed what I suspected.

JPC


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## Matt @ ScapeEasy (2 Feb 2019)

jaypeecee said:


> Hi Tim,
> 
> Thanks for the reply. I see what you mean - after just over two hours, CO2 is down to 4ppm. Not exactly conducive to plant growth! So, it's almost irrelevant what proportion of this figure is produced by the fish.
> 
> JPC


And 4 hours to build back up to near original levels! I always wondered how long to build back up


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