HELP!!! <Continued Problem Getting Much Worse, 3 weeks left of flower!>

I am Having a continued problem with my grow in mid flower, I have tried flushing, adding cal mag, potassium, & Phosphate... bottom leaves are yellowing,dying and falling off, and pretty much all leaves are curling twisting And Browning at ends and it's spreading like wildfire, even down buds leaves! I'm starting to suspect disease or fungus/bacteria of some sort. have a minor fungus gnat infection, but nothing too bad.Running 4 trays,2 grape ape and 2 cherry pie, cherry pie seems to have it worst. Ruined my last crop of cherry pie and I Need Some Advice From growers not willing to take first shot in the dark.. Help Please! I had drainage issues up until about 4 days ago and flushed but shit still seems to be twisting and rusting bad and Swelling spurt is coming soon...
You can see problem getting worse and worse from a couple weeks ago @.
https://www.rollitup.org/marijuana-plant-problems/549048-rust-fungus-nute-burn-deficiency.html
&
https://www.rollitup.org/marijuana-plant-problems/548121-need-ur-help-w-mid.html

Thnx In Advance & Respect For Problem Solvers!

the tops are burning under the light and i think your pot is way too small for flowering encouraging salt build up (rusty look to the leaves).

Ok so I put pots on bricks an did a mega flush, lotsa dirty water drained out at high ppm's and ph, so Now I'm gonna start re-nuting medium. what do you think about amount of cal mag and what not for last 3 weeks of flower as I usually don't use it at this point but plants seem to have a mag deficiency..