Get Seltzer water ($1) which is essentially Water with CO2 (not tonic water or any other carbonated waters) and put it in a spray bottle and spray your plants 2x day turning off the fans for 1/2 hr. so it gets a chance to take it in. You will see the bubbles on the leaves. Only put enough in the spray bottle per day and buy the little canada dry 6 pack bottles because once you leave it the spray bottle or open the original bottle it begins to dissipate(spelling?) and then you bought all this seltzer water and it's pointless after three days. If you go to youtube and watch Mr. Green videos he will show you his CO2 setup in one of his 9 videos and he sprays with Carbonated water daily. I began doing it during my last grow and the plant became healthier than when I started.