Help! Temperature issues in large grow room

While were on the topic of CO2...a new issue has risen. I am running a 50lb co2 tank with Titan Regulator and Apollo CO2 controller. I filled my tank monday. It had averaged around 650psi all the way through yesterday when I left the shop. This morning when I arrived, my tank was empty. It was fine all week then suddenly emptied. This is the second time this has happened.

I am thinking that it may be two possibilities. One, the wall mount air conditioner is not truly recirculating and is expelling co2. Two, the apollo is not turning the co2 off at night and the exhaust fan is pulling the co2 out.

IS there anything else that could cause this???

I may have figured it out. My timer was set to ON not AUTO so the lights were on 24 hr per day...I have the exhaust fan setup to turn on when the lights turn off, so the exhaust fan would come on but the lights stayed on so the Apollo didn't turn CO2 off, therefore sucking all my CO2 out of the room! I need to pay more attention to the small details!!!!