I broke down and bought an $80 regulator, tank, and other supplies
last March. The tank is only a ten gallon, running about eight hours
a day, about a bubble a second in a 75 gallon tank. It's been
chugging along for almost 10 months now much to my delight. I had no
idea the CO2 systems were so cost efficient once you get past the
initial expenditure. At only $12 or so to refill the tank it's a hell
of a deal. Obviously, I realize only running it 8 hours a day is part
of the savings, but the plants are really benefitting.

How long can y'all keep your CO2 going between fill-ups?

Andy