I use a ph controller on a planted tank but paid little attention to the kh/ph tables and am not bothered about actual ph value although I do calibrate the controller now and again. I use the controller as a means of hitting a certain co2 level based on the response of the fish. What I do is decrease the ph set point slowly (e.g 0.1 units per day) and carefully observe the fish for signs of stress e.g. increased respiration, at that point I then back off by about 0.2 ph units. The whole system can be linked to a timer so the process only takes place while the lights are on and this will give the benefits that Tom mentioned. You will find that the fish are most likely to show signs of stress at the beginning of the day when the lights haven’t been on long and O2 levels are lowest. If you are going to use this method then it is worth making sure your ph probe is in reasonable condition and responsive, and please take it very slowly and be careful with your fish.

Cheers
Neil