They will go to dwc later, thats why hydroton. So maybe its nutrient burn ?That media doesn't go well together... rockwool and hydroton are very different. One needs watered almost constantly and the other can be over watered.
Pom is to high IMO and you should NEVER spray plant under light. It can burn the leaves
Looks to me like old damage so I wouldnt really change anything to much. Adjuat the ppm and ph if needed. And absolutely do not spray them.They will go to dwc later, thats why hydroton. So maybe its nutrient burn ?