George Pontis wrote:
You do not require an automatic pH
monitor/controller. Instead you can set it up at some initial rate, say 1 bubble
every two seconds, then adjust up or down as needed to get to the level you seek.
If you know your KH, then you can determine CO2 by measuring pH using your
favorite test method. It may take a small adjustment once or twice a day for three
days to establish your setting, but once done it will remain stable.

I find my that bubble rate varies depending on ambient temperature. The
higher the temperature, the lower the bubble rate. One day, I set my
needle valve for 2 BPS. Ambient temperature was 25 degrees C. The next
day the temperature rose to 30C. I got 1/2 BPS. I set the bubble rate
back to 2 BPS. The day after it went back down to 25C. The bubble rate
was now 4 BPS. This must be something to do with expansion of metal
parts or cheap CO2 valves. I'm not sure if this is everyone's
experience, but I have to use a pH controller to keep the pH stable. It
was just far too much stress without it.

Nikki