Just to add my bit, from what i've read 40watts per sq foot is what you should be looking at, so a 400hps would be fine for a 3'x3' area, allowing you to flower 9 plants. Apparently when you go over 40watts per sq foot light starts being wasted. But i'm not sure if the use of Co2 would allow the plants to use more light so you could up the 40watt limit of deminished returns. 100 watts a sq foot seems too much to me tho weed4life