I have this exact combo. It is a little confusing at first on the alarm sensor. I have the set point at 7.6 and that means the alarm is on, allowing the soleniod to be open and CO2 flowing to the reactor. The pH monitor shows 8.0 mostly so the alarm will always be on. When I collect some of the drip water and check the pH with the monitor, it drops to 6.7 and the alarm turns off thus shutting the CO2 into the reactor. Once I place the probe back into the sump and the pH increases to 8.0, the alarm kicks on and CO2 flows.