Wild question--CO2 from fish=what plants need?

[kamanut]

Here is my wild question.....so plants need CO2 to thive. Fish give off CO2 as they respirate. So is it possible that if you overstock a tank enough, you could equal the amount of CO2 from fish respiration that your plants need?

 

[Essjay]

A non-overstocked tank will provide enough CO2, it doesn't need to be overstocked unless you are growing plants that need a large amount of CO2.
Plants also respire and make CO2 24 hours a day and they don't remove it at night, they only photosynthesise when the light is on.
Micro-organisms in the substrate break down uneaten fish food, fish poop etc and make CO2 as a by-product.

 

[kamanut]

A non-overstocked tank will provide enough CO2, it doesn't need to be overstocked unless you are growing plants that need a large amount of CO2.
Plants also respire and make CO2 24 hours a day and they don't remove it at night, they only photosynthesise when the light is on.
Micro-organisms in the substrate break down uneaten fish food, fish poop etc and make CO2 as a by-product.

Right, I get that. I just question why people use CO2/Excel then? If you could just overload your tank a bit, wouldn't that make more CO2? Or can no amount of fish equal the amount some people need for planted tanks?

 

[Essjay]

When a tank has a lot of so-called high tech plants, CO2 is usually used. These are plants which need a lot of light and fertiliser and they need a lot of the third requirement - CO2. Often these tanks are intended as aquatic gardens and they contain only a few fish as the plants are the main attraction, so less CO2 made by fewer fish, and less fish poop etc to be broken down.
With plants which do not require this intensive culture, a sensibly stocked amount of fish is enough.

 

[Byron]

Essjay is correct. Another aspect of this, is what happens to that CO2 at night. All of us with plants in an aquarium know that CO2 builds up at night. Respiration of not just fish but also all plants and some species of bacteria results in CO2, and while plants take this up during the daylight (assuming the light is of sufficient intensity to drive photosynthesis) nothing is taking it up during darkness (darkness meaning during the night and whenever the light is not driving photosynthesis). So a fish load greater than what the tank's biological system can easily handle will mean CO2 poisoning of fish during the night.

While I was typing the above you posted a follow-up. Those who use CO2 only have it on during the daylight, usually timed with the tank lighting. This is because of what I said above, that during darkness it would easily poison the fish. Most high-tech planted tanks if they even contain fish (many do not) also have additional surface disturbance (from filters, etc) during darkness to actually help drive the CO2 out. As for Excel and similar so-called liquid carbon supplements, these would be dosed minimally so all of it will get used during the daylight--at least that is the intent; no one should ever use these products because of the very serious harmful effects to using these chemical substances, but that is another issue. The point is, that CO2 is poisonous to fish so it must be very low at night, because it is naturally building up during darkness. The more fish in the tank, the more danger from this natural build-up.

And to your last question in post #3...this depends upon the plant species and their number. Some plants need more nutrients which includes CO2, others need less. But CO2 is rapidly taken up by plants which is why it is usually the first nutrient to become depleted during the day. We get aroound this with the lighting/nutrient balance and the plant species/numbers. The tank light cannot be on longer than thee available nutrients including CO2 because once the nutrients lessen below what the plants need the photosynthesis slows and may even cease, and algae then has the advantage.

 

[kamanut]

Essjay is correct. Another aspect of this, is what happens to that CO2 at night. All of us with plants in an aquarium know that CO2 builds up at night. Respiration of not just fish but also all plants and some species of bacteria results in CO2, and while plants take this up during the daylight (assuming the light is of sufficient intensity to drive photosynthesis) nothing is taking it up during darkness (darkness meaning during the night and whenever the light is not driving photosynthesis). So a fish load greater than what the tank's biological system can easily handle will mean CO2 poisoning of fish during the night.

While I was typing the above you posted a follow-up. Those who use CO2 only have it on during the daylight, usually timed with the tank lighting. This is because of what I said above, that during darkness it would easily poison the fish. Most high-tech planted tanks if they even contain fish (many do not) also have additional surface disturbance (from filters, etc) during darkness to actually help drive the CO2 out. As for Excel and similar so-called liquid carbon supplements, these would be dosed minimally so all of it will get used during the daylight--at least that is the intent; no one should ever use these products because of the very serious harmful effects to using these chemical substances, but that is another issue. The point is, that CO2 is poisonous to fish so it must be very low at night, because it is naturally building up during darkness. The more fish in the tank, the more danger from this natural build-up.

And to your last question in post #3...this depends upon the plant species and their number. Some plants need more nutrients which includes CO2, others need less. But CO2 is rapidly taken up by plants which is why it is usually the first nutrient to become depleted during the day. We get aroound this with the lighting/nutrient balance and the plant species/numbers. The tank light cannot be on longer than thee available nutrients including CO2 because once the nutrients lessen below what the plants need the photosynthesis slows and may even cease, and algae then has the advantage.

Thank you for this. Very informative.

 

[PheonixKingZ]

Definitely don’t overstock a tank, just to get sufficient amounts of CO2.