Poor CO2?


Lifetime Charter Member
Lifetime Member
Jan 2, 2008
I am relatively new to the planted aquarium world and I have noticed in all my reading that 'poor CO2' gets the blame for much of what ails a planted aquarium. Particularly BBA and surface scum.

Well, I must have poor CO2 because I have both. My question is, what are we calling 'poor CO2'?

Using the kh tables my CO2 is staying right around 15 to 20 ppm. Does that range need to be narrower? Maybe 15 to 20 ppm is too low for 216 watts of light over a 75 gallon tank? I run the lights for 8.5 hours per day.

I would appreciate any insight you might have.


Lifetime Charter Member
Lifetime Member
Jan 24, 2005
Sacramento, CA
You cannot determine how much CO2 is in your tank water by using the KH/pH tables. Those tables will almost always overestimate the ppm of CO2. Use a drop checker to get a much more accurate measure, which is still a pretty crude method. The drop checker can be used to tell you you have about 15 ppm or about 30 ppm of CO2, or any other concentration by using the right KH of water in the bulb. Personally, I think 30 ppm is the ideal goal.