I dunno what ur guy is telling rust? what? noooo dont harvest early!! keep it 12 12, flushy your plant roots with distilled water, clean out your res, and leave distilled water in there for 2 days. this will flush your plant. If your using tap water make sure to let it sit a day or two to evaporate the chlorine. If your flowering, just use the bloom mix, no grow/veg is needed. This looks like a deficiency but can be misleading. after you flush the plants add in half of the nutes you were using before, and let the plant adjust from shock. You should see any burn stop at this point, get some epsom salt too and add in a table spoon per 2 gals with the 1/2 nutes your using. and up the nutes after the plant starts to show signs of good growth. Your in a shock stage right now, so u need to nurture her back into shape. You may have locked up your plant with to much nutrients, u can tell if the new growth is just as bad as the old. If the lower leaves are the problem then it could be a deficiency, by the looks of the burns your locking up nutes in the leaves, they burn the plant, a deficiency will not burn as quickly, you will see the leaves change color then see burn, but some of your leaves have just burns.