Ok, long but stick with it...good info to know
Originally Posted by Wasserpest
A bubble of CO2 here and there doesn't starve aerobic bacteria of oxygen. CO2 and O2 are not mutually exclusive. Adding CO2 doesn't reduce the O2 content of the water...
I couldn't help but correct you wasserpest
...It's like a thorn in my flesh (I'm a chemistry student). It isn't a matter of CO2 decreasing O2, because your right they are "mutual", but the CO2 "blocks" the O2 from getting to the bacteria.
Here's some hard evidence: The Lake Nyos tragedy. I'll make a long story short: In August of 1986, a cloud of gas suddenly boiled from Lake Nyos in Cameroon killing nearly 2000 people. The lake is thermally stratified; layers of warm water at the surface sit on top of colder, denser water on the bottom. Normally the lake remains this way. For reasons unknown, CO2 has been supersaturating the colder water at the bottom for thousands of years. On that day monsoon conditions cooled the top layer and caused the lake to "overturn" its layers and releasing the huge amount of CO2 into the atmosphere. Basically what happened is that the CO2 "out-diluted" the O2 and the O2 was blocked from being diffused in their lungs. This is not only true of CO2 but of all dissolved stuff.
Originally Posted by Rex Grigg
What's the practical difference of running the CO2 into the filter and running it though a diffuser? If you end up with the same amount of CO2 in the water column it should cause equal harm to the bacteria...
Yes, I thought this way first, but it isn't that simple. When you diffuse the CO2 in a tank or in the filter, there are two big differences; the tank has a lot more volume than a filter. Concentration is measure by the inverse relationship of two variables, amount/volume. When a bubble of CO2 is diffused into the whole tank, it has a lot of volume to cover but in the filter, the same bubble only spreads to a relatively small volume, upping the concentration considerably. This high concentration is only temporary for each bubble, since the CO2 rich water spills back into the tank diffuses further, but this water still has to go through all the bacteria and has the same effect as described by the Lake Nyos incident. Sorry if it was confusing, but being blunt, I know I'm right.
Ok, despite all this I see no problems with this method of CO2 diffusion. Ace, Wasserpest, and Rex I believe reflect experience of most here and myself that CO2 doesn't pose any problems to the bacteria in the filter. Everything I just explained is correct theory based on the most fundamental chemistry laws, but for practical purposes it obviously doesn't pose any problems; the amount of CO2 used in aquariums just isn't enough to suffocate the bacteria.
BTW, here's the link where I read not to put CO2 in your filter (click CO2).