Has anyone done this, or heard about it.

[marijuanamat]

brewers yeast mixed with sugar and water gives off loads of CO2 and its cheap as hell.

[kramllehctim]

There are some real good ideas here about CO2, and I herd it will increase your yield for sure. I think as much CO2 that's in the air already, JUST VENTILATE LIKE A SOME-BITCH! LOL! Well, that's what I do. I like the brewers yeast and sugar trick though, that kicks ass! Peace ya'll