over watering....
are your plants still in rockwool cubes?
Oh man .. I am gonna catch shit for this....
Go bye a bag of Miracle grow and a 3 gallon pot... and some perlite
fill the bottom of the pot with perlite.. you will need to place a piece of newspaper down first to plug the holes... or else the perlite will run out the bottom...

put the cube in the pot full of dirt....

water thouroughly.. maybe a gallon of water...

put CFL over pot... make sure there is a fan on in the room.. doesnt need to be pointed at the plants.. just something to make sure the air is moving...

keep the light 3 inches from the top of your plant..

pray...

you now have a winner...

i love you