I have a problem with large fan leaves curling up and dying. I had thought perhaps it was spider mites, but I can't find any. Further confusing the issue is I have two varieties side by side HOG (primarily Indica) and OG Kush. The OG does not seem to be effected. The plants are in veg, 4 weeks old, 5 gal, DWC, ph 5.4-6.0, Tetraflora nutes, ppm 1500-2000 under a 600w MH. The pic's show the leaf, a 30x shot of both the topside and underside. The 30x shots basically show an 8mm wide area of the leaf. I see a lot of small white dots that I first thought could be spider mite eggs, but no matter where I look I can not find a mite or for that matter anything moving.
Your PPMs are WAY to high for DWC brother! Flush with superthrive and PH balanced water and do a res change with 6.0 PH, 650-750 PPMs and if you are not already, start adding silica at the rate of 1 tsp per gallon.