What is Causing This?

i had happy frog do that with my seedlings... replanting them in some dry happyfrog tends to do the trick but i did find out after i bought a good ph meter that i was using water above 7.6 on ph.. and i found out a lot of bottled water is very high in ph... with water that high u need to lower it but make sure u dont repot and then water with high ph water, best stunted in those container than to waste the happyfrog bc of poor water... that looks like a phos deficiency cause by high ph cause nute lock out which is important for root growth(yes happy frog has plenty of phos for root growth, which is important to a healthy plant but no matter how much is there if the ph isnt right its not going to be absorbed, so this can create weak roots, which means little leafs growth/susstainability, which doesnt get the nutes needed whihc then puts the plant in survival mode till conditions are better. fix ur ph before u do anything else., get that light away near 24 inches away.

Well once these were re-potted they did fine. When taking them out of the cups, the soil was very wet, and the roots were all matted along the sides. They were repotted and not watered for a few days. They perked right up and seem to be doing fine now. A couple sets of leaves were lost but new growth is looking good. They were definitely over-watered. It's hard to get the watering in small cups right, because if you don't water them soon enough, they can dry out very quickly and shrivel up and die.