Some sort of deficiany?!

400 watt hps water culture grow- Been using Nutes as they say...dont know brand of nutes or anything....someone conned me into them instead of foxfarm and using them up before I make the switch.....anyway! they are in a box with 32 other plants all the same age. This started about a week ago and is really only on the first set of fan leaves that the plants have grown.....I treated it as mag Deficiancy and it appears to have been getting better but I want to double check. The new growth on plant shows almost no signs of this at all

What is this!?!!

If the oldest and lowest leaves, like the pod leaves and the first single-bladed leaves, are in the worst condition then it's probably nutrient burn. If those leaves are fine, the problem is likely Phosphorus deficiency.