From what I have gone through this year with a difficult grow. Its a combo of a few, 1. Burn, 2. Cal mag deficiency, 3. Ph imbalance. In soil make sure you keep 6.2-6.8 ph give or take and keep your ppm levels as even as possible. Honestly I would flush like crazy for starters. Is a 3-5 gal pot you should flush with 3+ gallons of water, slowly but diligently. Salt build up is a killer and you might want to do it for two days, after that give the plants five or more days to completely dry and give the roots lots of fresh air. If you dont have cal mag go get some asap. When you begin using nuts again do a little less than before because its always easier to add than take away. Its going to take time but patience will pay off. Good luck sir, keep updating!
Safest feeding regimen is Feed, water, water, water, Feed and take notes so that you can adjust as needed for future grows. So if you see a deficiency at week 3 you'll know to supplement next time at week 2. Here's some other tips for troubleshooting:
Is only one leaf affected? Yes = Invaders (bugs, mold, mildew), No = continue
Are leaves clawed, puffy or bumpy? Yes = Over Watering, No = continue
Are the leaves droopy, thin and curled under? Yes = Heat stress from light, No = continue
Is the plant growth stunted and leaves/tips yellowing? Yes = Nute Burn, No = continue
Is there any purpling cupping or folding leaves? Yes = Mg deficiency (purpling is also an early indication of over watering)
Are leaves drooping but still flat with no discoloration and media is dry? Yes = not enough water, No = continue
Are leaves drooping and media wet? Yes = sudden wilt, so sorry for your loss
Note that a few random leaves dying is perfectly normal and at about week 6 - 8 in flower you should see more leaves start dying off which is normal. Prior to weeks 6 - 8 any more than a few random leaves is a problem.
Micro def - show at top of plant first (rare, if you have micro deficiency you probably over watered and damaged roots except in the case of Mg which is the most common micro def)
Macro def - shows at bottom first (N is most common Macro def especially in early flower - refrain from dropping the N until after the stretch)
Too Many Nutes - shows at the leaf tips first
Too Few Nutes - pales from the bottom upward (typically N deficiency but also can be attributed to not enough light, for example when using CFL or incandescent)