Assuming your pH is still on point, that looks like a cal/mag issue. If you have a cal/mag supplement I'd suggest adding it to your feeds. If not, then some epsom salts and molasses. Both can be mixed into your feeds, 1 tablespoon of each per gallon, or the epsom salts can be given as a foliar feed, 1 teaspoon per quart of pHed water. Mist both sides of the leaves with it daily for about 3 days.