You probably know more about growing than I do... but the usual suspects are too much water and too little water. I've also read discussions in regards to 24/0 lighting, and some people strongly believe that any plant needs a "rest" period, that they have evolved to utilize dark time for specific metabolic functions (the specifics went over my head). When you say "after all night under lights" I'm assuming you are running the lights 24/0? If so, maybe try 20/4 and see if that gives them time to recuperate?