12 inches is too close for your light at this stage of growth, you see the serations curling up...thats a sign of light stress. Too much light can cause all kinds problems. I looked at your nutrients and im seeing only .23tsp per gallon of calmag.....i'd go 1tsp per gallon. Feed ph looks good, however also check your runoff ph to make sure its not out of whack at the root zone. I'd put the lights at 24 inches and within a few days you will see a difference. Happy growing.

I'm sure peeps will agree that's a Calcium deficiency.Get some Cal-Mag.Is that Coco your growing in,and are you using Coco nutrients.If your using normal nutes that's your problem and you may need Calcium all the way through your grow.You should always try and confirm it somewhere else though.Iv seen some dodgy advice on here.

so sad. I feel for you. when they look very healthy and then start doing things like that. :( sorry, I read something recently about when it starts and looks like that on the side but I can't remember what it was. and since it doesn't just start on the side for you but also in the middle, that would probably be a false statement as well. or maybe two different problems. good luck. someone here will definitely give you a solution as a response.