Hehe tell me about it, Co2 is a lovely idea! but very hard in practice to pull off without air con!
I have been thinking about this problem for a while, I have a 600w in cool-tube in a 1m x 1m x 2m with 6" in-line and a 4" carbon filter and fan each with own duct but it still vac's the air in 30 sec
I would have thought it imposable in your size grow to use Co2, but it depends how rich and mad you are?
I did have one random idea that I got whilst watching a survival TV show on SKY, apparently people put clear plastic bags over plants in the desert to make the plants sweat excess water from the leaves and collect in the bag for pure drinking water... my thought is MAYBE... its possible to put a clear plastic bag over the section of the plant your most wanting to excel in growth ie. main cola's, and spray in ample Co2 and tighten the seal of the bag to hold in the Co2, forcing the plant to use the Co2 provided, of course.. the plant will most likely sweat too, just like the desert plants so a nuitrient should be added to counteract the extraction of water and or possibly higher the humidity after for a while to counteract things? then after 30 - 60 min's or so release the cola/section of the plant from the bag and in theory it should have worked... on a small scale this should be effective, however on a large scale time consumption would be immense, but then again (if on a large scale) C02 would be much more under control..food for thought anyway's let me know what you think. I mean it is just a theory but I see no reason why it shouldn't work let me hear your thoughts!?? - STELTHY