Temps would be to high for my liking.
Do you have em in rockwool cubes in the system?
To me it looks like calcium or mag lockout, usually due to salt build up or ph flux in medium. i like to spray up until 3rd week of flowering in hydro with cal-mag supplement (1/4 teaspoon to a gallon of water for a spray) Also in rez but at a (5 to 10 ml per gallon).
Also what are temps in your room if to high also can create heat stress and take up more water than nutes. bringing me to my next question. how often are you topping off your rez? while water evaporates ec rise's because salt doesnt evaporate, i add r/o to my rez daily to keep topped up always. if i need to adjust ec i top with 1/4 strength nutes.
Hope this helps
ohh ya what is your huidity%?