The question is how is your CO2 system being setup? At night, I have an air pump turned on until 30 minutes before the CO2 comes on. My soleniod is connected to a timer. If the either the timer or the soleniod stopped working, the air pump should be enough to prevent massive gassing. There was a week my CO2 was turned on for 1 hour at some times around 1 am because I have accidentally pushed in one of the tabs on the timer. I didn't notice it for about week until I actually checked the timer.