Every day i check my babies and more and more leaves are dieing they turn yellow and the tips are turning brown and curling up.... What could this be I think its preventing the buds to grow to the full extent i have 3 lights on top 2 42 watt cfls and 1 20 watt at the bottom i have a 42 watt cfl i water them every 2 or 3 days sometimes a little longer and i have an air purifier in there when lights are on...when lights are off there is no ventelation and thats what i think it is.. any help please?