Deficiencies my aunt Fannie. That's nute burn going on there.
A potassium deficiency would be showing on the oldest lower leaves first but some people think everything is low K. Those leaves look great so it's not low K.
Pour enough pH balanced water through each pot to get the volume of the pot as runoff to reduce the buildup of nutes in there. They don't need high levels of nutes this far into flower so give them a few days before watering again or until they dry down a bit then go easy on some bloom feed and use epsom salts instead of calmag. They want more Mg, S and a bit of K. Should be plenty of Ca left and they don't need lots of that any more either. Nor do they need any N and they can scavenge all the N they need from those dark lower leaves. Can steal P and K from them too.
I've seen this kind of damage a lot and it's generally because the upper leaves are too warm so the plant is sending more water their way. Often the jagged edges of the leaves will bend up making the leaves look all 'saw-toothed' which helps increase evaporation. When nute levels are fairly high nutes get left behind until it becomes toxic and fries the edges. Just short of toxic salts buildup where the whole surface of the leaves will fry like that. That could happen yet.
This stuff takes time so I'd feed about 1/3 less next time for the whole grow.
Good luck!