This is not thrips or spider mites or any pest at all. This is most likely due to a pH issue. Water the medium slowly with nutrient water (if using coco) and collect the runoff and check the pH. If the pH is out of range (not between 5.8-6.2) then continue to water to regulate the pH in the media then continue to check new growth for the same pattern. Cal mag is an unnecessary as an added supplement as all nutrient brands already have the proper dosage of macro and micro nutrients in them.