This is what I do with my DIY co2. I have it all set up on timers. When lights go out, reactor powerhead turns off, effectively shutting co2 off (it just bubbles out of tank) and at same time airstone comes on to add oxygen for night. In morning airstone turns off a couple hours before lights come on. Powerhead rector comes on at same time giving co2 a couple hours to build back up to 30 ppm for when lights come on. You could do same thing only you would have timer for whole co2 setup where mine is just for reactor.

Good luck, Bill

PS
Airstone could probably wait a few hours after lights to turn on because there is plenty of oxygen from photosynthesis/pearling.