I hate to hijack the thread but can you elaborate a little more on running it 24/7 for people with hard water? What you define as hard water? I run Co2 for 8 hours and the drop checker is always green to yellow, even in the morning, and I'm using certified 4kH water. Should I try running it all day/night?An electronic device which will turn on and off the gas flow. Lots of folks will only run the CO2 when their lights are on. If you have hard water, you will find this doesn't do anything for you, as you will probably need to run it 24/7.