I'm wondering if you are burning them....are you misting them with the light on? I'd also check the ph of your soil runoff and see what it comes up as....Don't know enough about soil to really offer anything....sorry.....looks like possibly ph lockout.

Here is an excellent troubleshooting chart.....hope it helps. Good luck.

Revised: The Complete Guide To Sick Plants,pH and Pest Troubles - PlanetGanja.com