my leafs!

use'n oxyponics system with hydroton clay pebbles, ppm 540 ph 5.8.... three part GH products with (thrive alive "green") my leafs mid way through my plants are turning yellow and my bigger older fan leafs are turning a brown yellow almost fragile to touch and kinda curling up some of them are?? flushed em went with half strength (ppm 540 PH 5.
I used to be a dirt fella lived by it loved but was curious about this oxy system so i tried it and it is amazing but! have'n a hard time with the hydro! never experienced problems with leafs turning?? what to do how to fix it?

Are the leaves yellow with brown crispy tips. Burnt pretty much. If so its phosphor deficiency. Curling like a claw is ph lock out. If the tips barely hook. That's an early sign of moisture stress or too much nitrogen.