Rockwool Pros???? Deficiency week 2 of flower??

Only thing that really caught my eye was your runoff EC was much higher then what was going in.

Tells me you may be getting to much dryback between your waterings. Which would raise the EC in the rootzone until you water again till your desired runoff.

Maybe try more watering frequency

As stated before that big of plant in that setup you could probably drip 24/7

Well im pretty positive it's just fungus gnats but I'll take a closer look. Just hit everything with nematodes to shut down the issue...

And I'm pretty positive at this point it was all caused by being rootbound/ not enough volume... i potted several plants in plastic post with gro cubes and all those pants seemed to be doing perfect, side by side you could see plants on the slabs were a much paler green... prob a late effort but at week 3 of flower i repotted all other plants on the slabs in pots with gro cubes... next round is in cubes and every forseable room will be here after. Plants were just too big for the 6x6x6 blocks which got choked out with the roots I'm thinking... not allowing even irrigation... something ha

Check me out, I'm gonna start crushing now that I can finally dial things in Haha @GrassRootsMarijuana on instagram

16' ceilings and using allll the space

Your roots were so thick that water could not penetrate into the root ball. Good detective work everyone! There comes a certain size when bigger may not be better.

You have both nutrient burn and def., your cube run off is off the charts. 2-6 is 1400-4200 ppm which makes me think that the cubes are getting to dry or plants are not uptaking food. More frequent watering would knock that out.
The purple Stem on the yellowing leaves starting from the bottom up is magnesium def. which could be a root aphid issue.
A mix of 2 gram epsom salt per gallon sprayed on underside of leaves should work in a day or so.
But both burn and def really makes me want to inspect the root zone for bugs.
After all those gnats start as large which eat roots