Yeah I was wondering the same thing. This has been very confusing to me. My test kit also give results in "mg/L" and I don't know how to measure that in ppm. For example my test kit says to add one drop of solution at a time until it turns a certain color and take the number of solution drops added and multiply it by 20 for GH and 10 for KH. My tests resulted in 11 drops of GH solution and 11 drops of KH solution, which I then multiplied.
Atmosphere ~ 300 ppm (0.3%)
Hmmm.....interesting, I guess different KH and PH readings can cause wide fluctuations to the point where the readings may or may not be accurate. I have a 10 gallon where water parameters tested monthly over 6 months would suggest that water parameters would be in the range considered ideal for plant growth, but the tank was plagued by fish deaths and very poor plant growth. As per drop checker the c02 level was 30 ppm, but as per on-line chart it was only 11.7 ppm. In that case, I was more inclined to believe that the on-line chart was more accurate, since black brush algae was one of the first types of algae to materialize and this usually materializes when
