Help, what the heck is causing this?

I am running 700 ppms, ph 5.9 , 6 1000, feeding twice a day. To much water? Nutrient issues, what

I'm having a very similar issue. Mine has been this way from seed day 1.

https://www.rollitup.org/marijuana-plant-problems/474488-whats-wrong-plant-should-i.html

Ya you know it's over watered this is why you have algae on the top
of yo cubes. I let'em dry out, just like dirt and keep the air moving
this will git rid of the algae. I water'em when they git lightweight
just like dirt. Did you presoak the cubes in 5.5 till the runoff ph is
5.8 for at least a hour, I do it longer. Have you check under the cubes
for roots? Here is some help at grodan's site for ya.
http://hydroponics101.com/sw58010.php

I water by hand from the top cause this gives the most control~

Thanks for the input. Cubes were ph, and I backed off on the watering, ones that were light I watered ones that were heavy i did not. Roots are shwoing at the bottom. When I backed off on the watering the problem seem to get worse. he were showing nutrient deficiency.

dam looks like a food issue, but with feeding twice a day i dont understand how that could happen.. maybe try feeeding just one a lottle more n see if it greens up. its showing signs of a sulfur deficiecy, but that is normally caused by nutrient lockout or a high ph so that shouldn be the prob. its jus wierd how it covers the entire plant. im sorry bro i hope you can fiigure out a solution.

When I do feed them, I do it till the cubes are heavy. The PH is 5.9 We had to use avid on them 2 weeks ago, nuked them hard, wonder if that had an effect.