The room isnt totally sealed. I allso find alot of strains dont like alot of Co2 when they are only a few days old thats why i leave it. But i know what your saying. If I have some real healthy babies and they are taking off quick forsure I will start the Co2 early. It just really sucks when your babies arnt liking the Co2 and they reject it. I think the key to any good crop is a great start.