need advice on plant problem

ive searched and searched and i think i have nutrient lockout and phos deficiency. using soil ffof cut with some mg amd perlite, 400hps, 2x4x4 tent. bottom half of plant leaves yelloe with brown-blck spots. day 30 flower. i had some heat issues when she sretched.

That's fertilizer burn that started from a young age.

i flushed last night and checked run off, it was at 5.9 ph, seems odd