Looks like heat stress to me. Try lifting the light another inch or two. They are babies still, so are very fragile.
nexusmick Reviewed by nexusmick on . Brown leaves on seedlings. HELP Guys: Need some help with what's going on with my 2 week old seedlings. Just in a couple of days the leaves started getting brown. Up to just few days ago had been using distilled water now have 5.5 PH tap water going and they are in rapid rooter cubes under florescent lights Ideas of what is going on and how to fix?? :( Help appreciated :) Rating: 5