Nute lockout or light burn?

I have a 600w hps in a 4x4 tent. Temps are good, under 80. But the center of the canopy seems to be lighter. I moved the light up from 14” to 18” to now 20”. It seems like the bleaching is worsening. Can someone confirm if this is light damage?

Just entered week 5 of flowering, day 33
Here’s the full canopy


This was almost two weeks ago at 20 days

I have maybe 17-22 days left, it's Critical Mass.
I'll do a flush in 3 days, then another feeding on on Friday/Saturday. Then another flush and feed then a final flush or two just water.
I'm using General Hydroponic flush to waste in Pro-Mix HP (soiless)
PH 5.9 - 4ml Micro, 8ml Bloom, 5ml flora nector and 2.5ml liquid coolbloom
Also using potassium metabisulfite to treat my tap water for chloramines.