OK, just did some quick checking on the levels of CO2 in the atmosphere. Apparently they are somewhere above 300ppm or higher depending on location, weather, etc.. Now I don't use CO2 injection on my tanks, so I don't claim to know much about that particular subject. However, it would seem to me,... and obviously I must be missing something,... that we could eliminate all that fancy CO2 injection stuff, simply run airstones into our tanks and get tons of free CO2 as a result. What am I missing here?? If you typically shoot for a few ppm's of CO2 in a tank for good plant growth, and the air outside the tank is loaded with the stuff, relatively speaking, why spend money to BUY it??? Clearly I don't understand the process.