Help Diagnosing This.

I'm having some issues with the leaves on my plants, I'm not sure if it's nute burned or a deficiency.

PH is at roughly 6.3 -6.5, temps 76-80F, been using 1/2 strength grow big and big bloom nutes for the last two feedings. I forgot to check my runoff before it got tossed out.
This browning/dying is slowly getting worse and I cannot figure out what it is.

Looks burnt. Lay off the nutes for a watering or two. If it's spreading quickly, a flush might not be a bad idea. I'd flush them some plain water and then put some Cal-Mag @ 5ML per gallon on them. Wait about 4 days and watch the new growth as well as watch to see if the problem still spreads. It probably won't.

I'm not an expert, but that's what it looks like to me and that's what I'd do.

Good luck.