This is the proper CO2 chart to use when measuring carbonate
hardness against PH to determine the proper amount of CO2 for your aquarium. I
recommend 7.0 (plants and fish from both acid and alkaline regions can all
coexist in 7.0 PH or neutral PH!) for the PH which as you can see by the chart
that your KH or carbonate hardness can range from 2-10 KH to hit optimum levels
of CO2 for your aquarium at a 7.0 PH. Also indicated are the optimum KH values
between 4 KH and 8 KH.