Originally Posted by pop
Just finished reading your three piece article about the nitrogen cycle and have got a question?????
Somehow I got the idea that the nitrogen cycle produces carbon dioxide if this is the case perhaps biological filters also produces carbon dioxide along with possibly fish respiration Do aquarium plants not in a state of photosynthesis release acquired carbon dioxide
What we refer to as the nitrification cycle is the conversion of ammonia to nitrite to nitrate to nitrogen gas. Most people stop after nitrate, but the cycle is only complete when the nitrate is changed into nitrogen gas which escapes into the atmosphere. Of course, in the aquarium other processes affect this too, primarily the photosynthesis of plants and the various bacteria in the substrate, some of which actually use nitrate and produce oxygen.
This nitrification process all on its own does not produce CO2, at least I am not aware of it doing so. The CO2 occurs from the breakdown of organics by other bacteria--this occurs mainly in the substrate, but also in the filter and elsewhere--and of course fish, plant and bacteria all produce CO2 during continual respiration day and night as well. The CO2 released by the breakdown of organics is far greater than that from respiration, which is why in a natural planted tank we tend to leave the substrate alone.
Plant photosynthesis takes in CO2 and produces oxygen. The plant is also respiring at the same time, doing the reverse, but during photosynthesis the intake of CO2 and release of oxygen is considerably greater than the reverse of respiration, provided of course the light intensity is adequate and the 17 required nutrients are available to the plants.