Originally Posted by asukawashere
Air does have plenty of CO2 LOL - otherwise we wouldn't have plants at all :P
The thing to keep in mind with CO2 is that it's actually heavier than the other molecules that make of air (mostly oxygen and nitrogen). So unless you have airflow to encourage diffusion, it'll tend to pool toward the bottom of a glass enclosure... as such, in a sealed environment, you could very well be getting somewhat hypoxic.
Fun Experiment: make a balance using two paper bags and a stick (yardstick, bamboo pole, broom handle, etc). Use the oldschool vinegar & baking soda combo to produce lots o' CO2 quickly and "pour" the resulting gas into one of the paper bags - the CO2 filled bag will weigh more than the unmodified one.
Interesting. Yeah, I read that air has something like 380 ppm Co2, where we strive for 20-30 ppm Co2 in our aquariums, so there is probably no need for Co2 injection in an emersed setup, although I think people inject Co2 in some hydroponic setups, but then again, they are probably not in a small glass box...