I've had my CO2 set up a couple of days now and I don't use a solenoid. 2 hours before the lights go on I push down the handle on the FE and put the pin back in to keep it open, 2 hours before the lights go off I pull out the pin and the pressure in the reg still keeps going for hours sometimes all night. I know its not that bad as yeast CO2 goes all night but providing the handle is up and its just the pressure in the reg that's gassing off it shouldn't waste too much should it?