A bottle, half full with water, add some yeast flour and sugar.. Put lid on, shake.. Open away from your face... Voilà.. Co2.Little more reading leads me to this co2 thing when flowering time comes. I have big tanks of that stuff already for the fountain soda. probably dangerous but gonna to some more reading on it to see if i might be able to use one of those tanks to pump some into the grow room LMAO.