You really dont need a controller with a reactor, most reactors now have dual chambers to burn off the co2.
I've found the easiest way to setup a reactor is to setup the flow per direcitons, ususally 1-2 lph, and the co2 1-2 bubbles a sec, give it a day to stabalize, and then test effluent dkh and tank dkh, and watch the 2 values over time, it's far more accurate than using the reactor ph as a baseline.