On one of the 150G's I have a 5lb cylinder with inline reactor at a bubble count that gos by so fast that I cant even count them. I get atleast 8 months out of it. The plant load is huge and very saturated with co2.

Do you mist or use an inline reactor? Also, do you have surface agitation? I know some people do on purpose because you can add more CO2 without effecting the fish that way.

I use an inline reactor with flow control valve's and mist at the end of the photo period.