Toxicity?

Clearly light burn.

Grab you some earthworm castings to put on the top medium for nitrogen and work it in. Then use cal mag plus at 1.25 ml per gallon instead of every 2.5 like it calls for. Do that every two weeks apart to fix the nitrogen and potassium issue in case because it’s one or the other. Try that and it will go away in a few weeks. You’re early enough in flower where it will fix itself

You should link your diary to the question. Do you own a EC/PPM pen to test the solutions strength your watering/feeding them with? Do you monitor the runoff of the plants in question?? That will give us a better idea of whats happening here. Some times lockouts happen from to much salt buildup in the medium. Good Luck!