Is CO2 heavier than air? The reason I ask is I have some Marsilea Quadrifolia that was languishing in my plant tank. I took it out and am growing it emersed. It's happy now but I was thinking that it would be easy to grow it in a CO2-rich environment — especially if CO2 is heavier than air. Do you see any problems with doing this? Justin P. Healy jphealy at sysconn_com