i totally thought about that for cheap co2 also. I read in a general hydro bookm (not pot specific) that some people do do it although they usually just use some sort of cheap sugar water mix and cheap brewer yeast not actually trying to make good beer. I thought about doing this because as you know the co2 activity almost completely drops off after about a week of fermentation so it could get expensive if your brewing a new batch of beer every week i know i drop like 40 to 100 bucks on a 5 gallon batch depending on what i'm brewing and what surplus supplies i have, but maybe you buy bulk malt and reuse your yeast stuff like that saves money. but yeah i have heard of people doing it so it is worth a try but i have know idea on how much it actually helps just because i am sure the co2 levels fluctuaate where as co2 tanks on timers are pretty constant. let me know what you find this really peaks my intyerest i have thought about it since i have started growing but because of illness i no longer enjoy much beer so i have not brewed in ages to actually give it a try. but if it works for you i may have to go with a cheaper version of the same i like the dry malt extract and water or even just baking sugar and water with some cheap dry yeast may not taste or smell good but should produce co2
