You might think it sounds silly, but i am a cook, and one thing you learn as a cook, when it comes to baking is that yeast gives off a lot of CO2. So much so that if you leave it unattended too long it will get so big it will ruin your dough or whatever else your working with. Yeast feeds on one thing alone, sugar, and it needs to be suspended in a solution to sustain itself.
Anyways like I said before it probably sounds silly and "ghetto" but i have two one gallon milk jugs on a rack above my grow. In them I put 2 cups sugar, 1 package active dry yeast, and then i fill it up half way with room temp water. I then use a needle i heated up to make just 1-3 tiny holes(depending on needle size) in the plastic cap on top of the milk jugs, then i outfit a piece of cloth over the top of the jug with a rubberband(to prevent it foaming over). I then leave these in my grow closet with the blanket sealing it all in and I give them a shake a few times a day when I check on my girls.
Everytime you shake them they bulge all out and you can hear the CO2 just pouring out of the top, and they will do this for up to two weeks before you just need to add another cup of sugar to keep the yeast feeding. I usually put my hand over the top top to seal it, then i quickly tip it upside down and shake it and then let it settle before releasing my hands and placing it back on the rack. I know cooks keep yeast out like this all the time to develop flavor in it, as long as the yeast continues to feed theirs no chance of mold or flies coming from it.
The best time of day to shake it is right before the lights go off because most of my fans cut-back at night, so the CO2 from the jugs can just float down on them as they make buds. I also didn't have a lot of grows to compare my results with these jugs to, but my friend has been growing for over 30 years and he claims after I got him to start using the jugs, that his plants were ready 2-3 weeks sooner than ever before and his plants got way bigger and had more nodes and he only used a couple of jugs and im not even sure if it was through the whole grow. This guy is the man when it comes to growing too, so now i go in there and shake them all the time and make sure the yeast has plenty of sugar.
P.S.-If you do use this method never fill the jugs past half way and don't over feed your yeast sugar, only add more when the jugs stop giving CO2 after shaking. Too much water or sugar could cause the top to come off them or just make some messy overflow, I have mine above my plants but over to the sides and not directly above for this reason. Also it only takes a little yeast to make more yeast, so you could make one jug with one packet of yeast, and just keep using a cup full from the old one to make new ones. So as long as your shelf can take the weight and you buy a $2 bag of sugar every few weeks, you can keep it going indefinitely and end up with like 10-20 of these babies unloading CO2. Hope this helps, I try not to spend any money I don't have to on my grow setup because money's ultra tight right now and this is definitely super cheap.
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