Originally Posted by Blue
Count the bubbles although it seems frustrating. 1-2 bubbles per second is often considered to be the exact amount. Or if you have a test kit, 20-30 ppm is a safe level for the fish.
Interesting. I have read from several sources and been told by numerous people on forums that you shouldnt let your Co2 drop below 30ppm in a planted tank or else run the risk of algae problems. Also, that most fish can handle Co2 up to about 90ppm.
A bubble counter is a must, IMO. I get about 60-90 bubbles per minute in my 55g with 100% diffusion. This keeps my tank between 50 and 90ppm. If you want to be able to test your Co2 levels, a good pH test kit and kH test kit (may be hard to find locally) are needed. Along with a conversion chart/program (free).