i have mine on a timer for 10 hrs and 14 off i figure i should get 3 months or more out of my cylinder iff i ran 24/7 maybe a month and a half my refill are 20dollars plants dont need the co2 at night why waste it and for the moring co2 level get up quick in my aquarium withing the hour and at night i didn a test one night when i was up late an it lowest point was around 12ppm day around 26-30ppm |