Sentral said:
Remember all that Nitrosifying and Nitrifying bacteria in your filter needs oxygen to function.
Adding CO2 to the filter inlet has no effect on the Oxygen content of the water. All gasses live side by side within the water column. It could also be argued that better CO2 diffusion, which helps the plants actually increases the Oxygen level since there is better CO2 availability.
Sentral said:
By pumping it full of CO2 this would probably decrease the effectiveness of the nitrification process. It isn't to the extent that you'll see major issues, but it may also effect the filters life span, especially on rubber seals which can go brittle.
Much better to get an inline filter IMO
The efficiency of the nitrate producing "nitrobacter. sp" is a function of pH and temperature. Their optimum pH is actually in the alkaline region but they can function in pH range from the mid 5's to the high 8's. Species of nitrobacter, such as Nitrobacter winogradskyi are "Chemoautotrophic" bacteria, meaning they are bacteria which obtain their energy by the oxidation of electron donors in their environment. Tthey fabricate their required organic compounds from CO2. So there is hardly a disadvantage in having a CO2 enriched filter. Nitrobacter also generally do not care whether the conditions are aerobic (Oxygen containing) or anoxic (Oxygen deficient). They can also function perfectly even if there is an absence of nitrite.
It's a similar story with the Ammonia Oxidizing (Nitrite producing) Nitrosomonas and Nitrosococcus which are also "Chemoautotrophic" and which generate energy by using the electrons liberated by the oxidation of Ammonia into Nitrite and which then uses this energy to convert CO2 to carbohydrates for food.
Nitrifying bacteria are in general, extremely athletic, versatile, and adaptable. They can change their behavior and their fundamental way of obtaining food based on the compounds that are available in their environment. That is why they are so successful. The only real disadvantage they face is in dealing with the low pH values encountered in CO2 injected planted tanks since they are optimized for alkaline conditions, but this has nothing to do with Oxygen displacement. These bacteria are happy to use both CO2 and O2 so there is no disadvantage in pumping CO2 into the filter. These bacteria also require magnesium as well as Phosphate and Iron, so they generally benefit in a planted tank which are abundant in these ingredients as discussed in
Nutrition and Physiology of Nitrobacter agilis
As far as the seals go, there ought not to be that much of a difference, since the water in a CO2 injected tank has CO2 dissolved in it, regardless of the method used to dissolved the CO2, which also makes contact with the seals. Having said that, filter manufactures often claim they will not honor warranty for seal leakage if CO2 is injected directly into the filter.
Cheers,
