Just a thought... It could also be a magneiusm deficiency. It looks very similar to a nute burn... I think maybe magnesium deficiency.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .That photo is of nutrient burn. This is a plant with a magnesium deficiency.
Magnesium deficiency looks VERY similar to a nutrient burn, but the leaves start curling UP. If you think you may have a Magnesium deficiency, foliar feed your plants 1/2 teaspoon of epsom salts to a quart of water. Mash up the salt, put it in a quart of hot water (not boiling!) and let it dissolve...then foliar feed it to your plants (spray on the leaves, top and bottom). Couldn't hurt. I was told to do just that, when a couple of my girls did that, and they bounced back in a few days. Hope I helped, friend. And GOOD LUCK!!