Planted Tank Guru
Join Date: Dec 2002
Location: Portland Orygun
A pH controller controls pH. With a CO2 system it does this by either allowing CO2 into the aquarium or shutting it off. It's not really needed. Many people here, myself included, run manual systems.
And you really do still need a needle valve even with a pH controller. Otherwise you are going to be blasting very large amounts of CO2 very quickly into the tank.
In the EQUIPMENT forum there is a post with pictures of how I split CO2 between two tanks.