For estimating CO2 content in water for the CO2 poll, I am using the formula: CO2(ppm or mg/l) = 3.0 * KH (dH) * 10^(7.0-pH) If anyone knows of a better correlation, I would be glad to include it on the spreadsheet. If you have measured CO2 levels, it would be also be appreciated, so I can correlate CO2 addition rate with CO2 solution concentration and against the above fornula.