fresh air exchange is important.
"air exchange has been the number one limitation to maintaining and controlling the growing environment optimum for your crop. Temperatures greater than 85°F are detrimental to overall crop quality in most cases. This temperature should not be exceeded in the plant canopy, directly under the lights, never mind on the thermostat hung on the wall several feet from the nearest H.I.D. light source. I cannot stress this enough. Yes, plants can metabolize faster under slightly warmer conditions in the presence of elevated CO2 levels, but this tends to contribute to less desirable developmental characteristics and physical appearances."
from a nice article...
http://www.gthydro.com/growroominformation.html
If you are growing in a hydro set up, you may want to check your water too. Not the ph, the ppm. I have hard water, and my plants would crap out on my like that too. I started adding h2o2, and cal mag.. the hard water locks out the magnesium. H202 I find helps break down anything that may be in the water, (yes it de-chlorinates, but that's not an issue here.. but it may be for you).
It looks like a few different things, but if you get your air and water straight, you will find things get alot easier.
Edit: the quote was taken out of context, but was only meant to demonstrate that it makes your plants look crappy... I'm pretty high, I know what I mean, but I want to make sure you do too