I have a sugar and yeast co2 generator I am experimenting with. I figure I need 1 per plant, but really in a 4ft by 4 ft tent, two plants get crowded so to add that third plant, I am turning to scroging. I use silica blaster from bontinacare I believe. The co2 generators work equally well on autos as well as photos, but I don't know if they make a difference as far as cola production/size go.