Reducing "P & N will certainly help control Cyano, more flow in the affected area will also help... Theres no real 'kalk per gallon' formula, basicly, kalk will reach a saturation point with a Ph of around 12.4, you can add as much or as little and the Ph will never get above that level. It really depends on the size of the container and the ammount of top off needed to compensate for eveporation. Idealy, you want to top off 100% with fully saturated kalk... When you notice a decrease in normal Ph, you know its time to recharge your dispenser.