Another way to use the results obtained from testing the pH and KH of aquarium water is to use this table to determine the level of carbon dioxide present.
Using this method my readings of Ph=7.2 and KH=6 gives a Co2 reading of 11mg/l. This is 4mg/l lower that the previous calculation, as to which one is the most accurate, I really do not know so I decided to take the mg/l reading for my aquarium as the mid point between the two, i.e 12.5 mg/l.