hey man, gkn here...i have no idea on your CO2 question, but let me just say, nice fucking work man!! you've done something very special my brotha...i'm a long time indoor dirt grower and have never had the money to build a setup like yours, one day...and i couldn't agree more about how much better organic soil is, you just can't beat that taste....
i'll have some pics soon of my new grow, but i'm trying a soil mix for the first time, it's a bag of ocean forest, light warrior, and planting mix with a shit load of perlite mixed in, like 2 five 5 gal buckets worth...it's called the moonshine mix, the plants don't need any veg nutes and in flowering you can add whatever organic ammendments you like....so far the little plants are really loving it...well, i'm in for the ride...happy growing.
GKN