I had to make a quick throw-up enclosure because I miscalculated outdoor daylight hours, they still go outside 5-6 hours per day. This is by no means a sealed enclosure, the bottom edges are sealed up pretty well with tape but the top edges breath...and the center of the top where my main lights are have gaps around the lights with a vent tube above them so all the heat rises to the top and is then pushed out of the enclosure around the lighting. This is all natural rising of heat for the most part but since the top of the lights are hotter than the bottom it naturally draws air, plus the circulating fan inside the enclosure. Since they spend some time indoors now, I have this 5lb. CO2 tank for an aquarium I am not using right now...it costs about $8 to fill down the road. It has a gauge for tank pressure, output pressure, plus a bubble counter for a really slow reading. I do not want to just pi$$ away CO2 and if I am to use it I want the money to be worth it. Connecting it to the back of the oscillating fan seems like a waste to me, a few T's in the hose seems like a better way to go so I can distribute it better? The fan will just blow it out around the lights depending on how fast the plants leaves can absorb it? If it is distributed with T's it will rise under the canopy and get absorbed more as it makes its way through? Although I think CO2 slowly sinks... What do you all think about the "CO2 Bath" method, this seems the most efficient to me. Shut down all the fans and flood the enclosure. I forget if it is just before/after the lights come on...