Hello all ...i had this same problem in my last grow...i have been doing everything by the book...as soon as i saw roots coming out the bottom on the 3x3 rock wool cube i put them in the pots added the rocks and set them up to flood and drain 3 times a day ...up until this point i was watering by hand2 times a day.... i put them in my ebb and flow ...this was Sunday evening ...by Monday night i could already see the new growth begin to turn yellow and some of the existing growth on the plants have also begun to yellow...its only Tuesday and they were perfect Sunday night ...i have scrubbed everything with bleach and disposed of everything that was replaceable...i thought i have kept them in the rockwool cubes too long last time (2 months) and they might have gotten root bound.... but they are just 3-4 inches tall and only 3 weeks old this time im so confused...what should i do ...???