Tom was looking for the KH, pH, CO2 table. The original(?) reference is in the Optimum Aquarium by Kipper and Horst. Here are two formulas you can stick into a spreadsheet that give you the table(s): pH as a function of CO2 concentration and KH value: 7.58+@LOG(KH)-@LOG(CO2) CO2 concentraction at a given pH and KH 10^(7.58-pH+@LOG(KH) for both, KH is in german degrees (standard units), CO2 in ppm, and pH in standard units. Mike Eckardt