Well I'm now a week in since adding co2 to my grow, and the tank is already empty.. I have a 20lb tank in a 10x5 sealed room. I have the ppm4 controller and it kicks on at 1450 and turns off at 1500. It seemed to me it was kicking on once or twice an hour for about 10-15 seconds. This is in veg so 18/6, the co2 is on 18 hours. I actually added the tank in the room on monday, and it ran out this morning, on sunday. 18*6=108 hours it lasted. So in flower it would have lasted 9 days. Hauling around these tanks sucks lol. How long do ya'll get out of your tanks?