I think your PH is a little high for hydro, optimum ph is 5.5-5.8

and I believe your plants are experiencing a calcium def. possibly look into your nutes and change brands

you can test this by treating with foliar feeding with one teaspoon of dolomite lime or Garden lime per quart of water, Or Any Chemical/Organic nutrients that have Calcium in them will fix a Calcium deficiency. (Only mixing at ½ strength when using chemical nutrients or it will cause nutrient burn)

it wont repair the damaged leaves ofcourse but it should stop the issue

here is an example of calcium just starting