The pots you are using are they the Jiffy peat pots? If so get rid of them they are a curse, I used them in my first grow and had to transplant them to different pots, them they started growing. Dont leave water in the tray, just wet the soil until some runs out the holes, then don't water them anymore until the pots get light in weight then they are ready for another watering. use a 18 hour light 6 hours complete darkness cycle, plants need rest. lighting could be the problem as well, use 23 watts 6500k cfl lights in clamp work lights kepp them 4 inches from the plants (150-Watt Incandescent Clamp Light-HD-300PDQ - The Home Depot) what day of the grow are you on? Day 13 I start using a light nutrient scedule 1 ml grow, 1 ml micro, 1 ml bloom 2 ml of cal mag (General Hydroponics Flora Grow, Bloom, Micro Combo Fertilizer set, 1 Quart)
Sounds like you may be over watering. Hope this helps.