Leaves looking 'wrinkiled' and curling up: PICS

Hello,

I have some 3 week old plants that have leaves curling up in a 'V' shape.. Also, the leaves on some of the plants have a 'skin' that looks like dry human skin. Like it's wrinkled. Not all plants in the garden are having this porblem. Try to see it in this pic:

I'm using 1/2 strengh solution at 150ppm.
PH is at 5.5-6.0
The plants are on their 4th node I bleive.
The plants are getting 6500k daylight CFL's about 1.5 inch away from plants at 2000-3000 lumens (measured with light meter).
The plants have recovering from being very sick with nute lockout.
The watering/flood schedule has recently been changed to every 4 hours.

What is the issue with these plants? I heard after nute lockout they usually need epsom salts.. is this true?

Thanks!