Problems critical kush

hi all done a few grows but having a problem with this one. Grow has been perfect run upto about a week ago where the leaves have been going yellow. Know I know this is normal (I'm 7 weeks in flower ) but leaves are going brown around around colas. Ph is good and I'm in coco using canna a+b hesi bloom booster in 20ltr pots under a 600hps air cool light. My other 2 cookie kush in there are week 7 too same schedule and fine? No fungus nats spider mite ect. Sorry for shitty pics hope you can work with them if poss...many thanks

Its maybe more sensitive to overfeeding than the cookie kush?

Try giving it less fertilizer and see if it help.

Would you advise a flush or just cut back a bit from recommended feeds

I mean flush then cut back not flush permanently

I would flush to leach out any accumulated nutrients and start feeding again with mild solution.