BIGGEST mistake is how often you flood!
You should be flooding 5 times in a lights on period!
This is considered a hydro style grow. The Rockwool needs to be damp and NOT dry out at all!
This IS causing a pH problem too! As the RockWool dries out...The pH is rising!
SO then. You have lowered uptake of K and Zinc (and other things) by high pH, too long. You also have way too low feeding availability, so they aren't getting enough to start with......
The plants are struggling to get what they need!
Cycle the system like this.
The first cycle right at lights on!
The last cycle right before lights out - (as the cycle finish's. The lights should go out) THis carries the Rockwool and the plant till lights on!
Space the other 3 cycles - evenly between the first and the last.....
Things will take off and you'll be very happy and so will your plants...
More points of order:
pH everyday at lights on! pH should run between 5.6 to 6.2.....Different nutrients are best available at differing pH values. The way I used to run hydro styles was to focus on a pH of 5.7 - 6.2....It is best to allow the swing from you setting it to it hitting at 5.7, to rise to about 6.1 -6.2 before adjusting it back down.
As the rockwool and the plant age. The pH will settle down and rise in pH slower.
The damage to the plants will not "repair". They will deepen in green from the needed N. The new growth will show nice fresh undamaged plant as it grows.....You will "see" improvement in 3-5 days.
Good luck