why don't u guys buy a few mid size 20oz CO2 tanks($30/each?) for paintballing they even sell at walmarts and get em filled at the same time(3.99each for a fill) on the weekends so it looks like u paintball on the weekend(ask friends if you can borrow their unused tanks, everyone paintballs once in their life!). I buy a pack of o-rings because as soon as i gety the tanks i pull/rip the o-ring off. then i slowly screw it into my paintball gun. without the o-ring it leaks CO2 through the little purge hole on the thread attachment. I hang the paintball gun on a hook above the circulating fan (thats on the ground) on the ceiling. leaking half the tank a day ( screw it and unscrew it twice a day if u have time) it will provide me with a visual difference within 3 days of this procedure. It always looks like that was the nutrient they have all been waiting for to thrive with a growth rate on average of 1.2 inches per day. Im just waiting to buy a big tank with an automatic release and monitor. GIVE IT A SHOT, those yeast contraptions seem like a pain in the ass for a just a daily fart of CO2. no offense i just cant imagine using that method. lastly my room is a 6 x 10 foot so i use half a tank a day. by no means is this scientifically correct it just seems to be the minimal amount i need with my circulation to see the massive difference. If i do a full tank a day it makes no diff.