The issue with the leaves are one of 2 things,
1. Light too close
2. Not enough calmag in your mix as using coco u need that bit extra as tho coco loves to absorb calmag
Boost your humidity too to the 50-60 mark, the damaged leaves won't go back to a healthy colour it's the new growth you want to be looking at, try using 10ml of calmag per 10L
like 1