I've got a 5# bottle with a Cornelius regulator and NV-55 needle valve feeding a Rex style reactor at a little over 1 BPS and my drop checker stays in the green. Ph is about 6.6 and kH at 4.0. I'm on my second refill (=2+ tanks) in 19 months. I think the key is a good leak free system and a good reactor to maximize diffusion of the Co2 into the water column. Forgot to mention, the tank size is 29 gallon.
Last edited by PMM42; 11-13-2009 at 03:43 AM.
Reason: Added more information