I use the CO2 bags if it helps. I've also experimented with yeast bombs too - homemade bucket w/yeast and sugar. I do not have a sealed room, or a CO2 PPM meter. I cycle my exhaust on and off via a schedule.
Exhale bags recommends if you don't have a sealed room to put the bag on the bottom of your tent to draw up through the plants.
Do they work? Hell I don't know man. I started trying them out on a whim to play around with. Guy on eBay who apparently lives down the road from the Exhale farm and gets them fresh he says. Sells them fairly cheaply. One thing to note - the 365 bags are supposed to last longer but they take about 3-4 weeks once you mix them to start really "working". I use 2 in a 4x4 and 1 in a 2x4.
So do they work? Again, I do not have any way to say yes. Or no. I do know that once I started playing with a homemade yeast bomb, I started getting larger plants. When I added Exhale bags to my grows I started getting my biggest yields yet. Last grow was 3 autos @ 9.9 oz, 13.4 oz and 20.5 oz respectively. You can check out my grow thread linked below in my signature.
Again, I do not know if the bags help or they just sit there laughing at me. Or whether when I added them, it just was at a perfect time when I became a better gardener. If CO2 PPM monitors weren't so pricey I'd like to monitor it, but I don't have one.
For me, it was one of those things that I just added for fun once I had dialed in my grows. So always recommend that first and not expecting a magic bullet. I'm perfectly fine knowing that it could be total snake oil. But I continue buying them because I'm totally superstitious. $30 for a bag that lasts 4-5 months is a cheap way to play around. They do add humidity though. So that's a good thing for me. YMMV.
