Light Bleach or Other ???????

I thought this was light bleaching at first but now Im not so sure. Only other thing I can think of is it's using up what it can to produce.

4 weeks flo
temps ok
ph 5.5 to 6.0 drift in three days
15 gal drink every 3 days
ppm high 1300s to low 1400s depending on water level
strawberry cough
1000 watters x 4
lights about 12 inches +/-
BC Nute Line Boost/Bloom
Roots,great
Hydo ebb flo
feed 4 times a day


Not all the plants are doing this and it does seem to be the tops. Thats why I thought lights. I don't really want to move my lights away any further Really the only times I remember my leafs like this was due to light I guess. What do you all feel it is

Mag defiency i Believe cause its starting from the top down an the veins are nice an green while the leaves yellow.
They use alot in flower.
Epson salts should fix em up.