Modern LED panels run cooler and push plants harder than old HPS, and the common side effect is calcium and magnesium deficiency showing as rusty spots mid flower. Coco growers see it worst, but even soil grows under strong LEDs can need a supplement from the flip onward. The nutrient notes on https://potentthcseeds.com mention this for their heavier feeding THC seeds, and adding cal mag at half strength cleared it up on mine within two weeks. Water hardness matters too, since RO water has none to begin with.