What to do?

not light burn, i promise. canoeing can be heat, but looks more like an overabundance of nutes to me. K-tox causing Ca-def and anything else. I have a nute calculator.. it'll add up all your products, follow instructions. Make a more informed decision.. if K is clearly not high in your feed and EC of runoff is ~1.5 ish, i am wrong.

It looks like heat stress. The upper leaves are curling up and with Brown edges but the lower ones are not. Lift your grow lights, It must be too close to the plants top. And put a mini ventilador blowing direct to the top of the canopy.

Looks like light burn / heat stress to me.. 12 inches with that size light.. yikes.. try bending that cola down and getting it lower or as low as the next lowest if at all possible.. Hope this helps friend.. Happy growing.. 👊