The best way to check the effectiveness of your CO2
saturation is with a drop checker. I am surprised no one mentioned it earlier. The time the bottle lasts is also dependent on the size of your tank. A 5 pound bottle would longer on a 10 gallon tank as opposed to a 220 gallon tank so it is all relative. The easiest way to check for a leak is to spray soapy water on your regulator and connection to the tank and look for bubbles. If the CO2
gauge is bad, it will leak undetected for months. The best way to check the regulator is to perform a leak-down test. If you have a welding supply store near you, they should be able to check out your regulator pretty reasonably. I get my CO2
from a welding supply store as well. I can fill a 10 pound bottle for about $15.00, and it lasts me 3+ months in my heavily planted 135 gallon tank.