So in my recent adventures Ive been working with sealed small cabs so CO2 has been a necessary issue to address. And I preferred something that was small and concealable and cheap. I feel I finally may have come upon a solution that others here may find adaptable to their setups. I started off with a simple Fluval Mini CO2 supply designed for aquarium use. https://www.google.com/webhp?source...=1&espv=2&ie=UTF-8#tbm=shop&q=mini+fluval+co2 I also got a cheap solenoid for about $10 http://www.ebay.com/itm/351833595674?_trksid=p2057872.m2749.l2649&ssPageName=STRK:MEBIDX:IT I also got a bubble counter. Went to lowes and got a $5 fitting to connect the fluval directly to the solenoid and now I have a cheap ~$45 CO2 injector system that can be hooked up to a timer or a monitor. The threaded co2 cartridges can be found for fairly cheap online. I understand that this isnt practical for many growers but for small cab grows, I feel its a far better solution than any yeast or other diy supplements. If anyone has any questions let me know, I will update if I have any issues with it but just thought someone might find this useful.