Last year on pbs I was watching about co2 yes is heavier then air it can even be seen as like a fog covering the ground in the morn were co2 is coming out of the earth. On pbs they were showing all the dead things that the co2 killed and there was a big lizzard that went to go eat one of them dead bodys that were killed by the co2 once he went down into the co2 he started to become very weak but right before he passed out he made it to the top of a hill and got fresh air and lived .The whole spot were the co2 was coming out of the earth was very lush and green and all around the lush green was nothing but a dryed up Desert.
That was the first time I found out more co2 = better,Faster growing , more green plants.
Last year I tryed co2 in my green house useing yeast all the plants that were right near it grew alot nicer then the plants on the other side of the gh. If anyone thinks that more co2 wont help.l I would say it try it and see for your self .If you dont want to use yeast try DRY ICE as it melts it give off lots of co2.
_-West-_