And catpiss you are correct as well. If your growing with a small 400 watt light or some cfl's its not gunna be worth it. But if you have stuff down (decent light, constant temps, perfect humidity) CO2 will seriously pump your plants like no other. We did deep water culture for a year with house and garden nutes. Had perfect temps, 1000w lights, perfect humidity, babied them everyday, and they still didnt do what I got out of this last harvest (this last harvest was in soil not hydro so that should tell you something)