Calcium deficiency.
Add cal/mag to your line up or increase the dosage if already using it.
Remember, what is showing in the leaves now, is a direct reflection of what was happening in the root zone 2 weeks ago.
Cure will take 10-14 days to show results, it won't happen in 2-3 days.
Damaged leaves will stay damaged, but new growth should be fine once you start giving extra cal/mag.