Dying Leaves? Help!

Hi all im new to this so i hope ive come to the right place, i need some help diagnosing, on the 5th week of flowering i started to get some sort of defficiancy, the leaves were turning yellow and the tips were turning brown, i thought it was Zinc defficiancy but on the 6th week and still not changing, any ideas? Im using soil with perlite, using BioBizz with the BioBizz feeding chart and also using Superthrive, using a 400w HPS..?

.......PH?

edit: you could probably use a flush, they'll perk up

https://www.rollitup.org/general-marijuana-growing/420048-nute-burn-deficiency-guide-diagnosing.html

https://www.rollitup.org/marijuana-plant-problems/422952-cannabis-plant-pest-problem-solve.html

Toxic Salts Buildup maybe ?