That is how I run my reactor and how I recommend people run theirs. To me the solenoid is a safety feature for a power outage nothing more. If you are monitoring your CA reactor using the controller based off of preset values, you are depriving your tank of something. If you shut the tank off, because the pH is lower than 8.4 then you are starving the tank of CA, ALK, Strontium, Magnesium, etc, etc. If you have your effluent line above the water line in your sump, then excess CO2 going back to the tank should be negligible. It will dissipate in the atmosphere before it hits thew ater. I use my controller for the lights, chiller/heater, wavemaker, moonlights, etc, etc, but not to control my reactor. Try it how PM suggested to run it and let it run for a while before you determine if it works correctly or not.If anything, you could have the controller turn the CO2 off if the pH falls below 7.95 or so. PH in the 8.4 range is at the upper limit for most people. Most people have a range of 8.0-8.3 or so. Good luck...HTH