take a quart bottle ... drill a small hole in its cap, maybe 1/8", doesn't really matter ... fill halfway with tepid water ... add cup of sugar, and a package of yeast ... add a bit of sugar every 2-3 days, it releases a surprising amount of CO2 ... the sugar feeds the yeast's organisms, which die, and give off C02 during their decomposition ... if you forget to add sugar the yeast organisms starve, and you have to start over with a fresh batch ... as said previously, CO2 won't make a visible difference unless everything else in your grow is spot-on perfect ... its probably the least efficient method of improving your plants, $-wise ... sugar and yeast are almost free, nothing to lose ... :smokin: