yellowing with brown burnt colored spot. any thoughts?

anybody have any thoughts as to the deficiency i'm looking at here? I'm guessing magnesium, but i'm no good with identifying nutrient deficiency.

I use rockwool w/ gh nutrients.
ph at 6
ec at about 12 or 13, 4 weeks into flowers.
Heat got out of control and probably sat at 85-90 for a bit. corrected yesterday.
tap water starts at 200-300ppm.

any ideas? please let me know if you're just guessing. Thanks!
 

Attachments

Top