Any idea??

Potted in canna coco , fed with canna coco A and B , rhizotonic and hygrozyme ,ph 5.7 - 5.8 for first few feeds but did feed at 5.4 on last feed as overdone the ph down . Surely one ph swing wouldn’t cause this?
Leaves that are affected also feel rough to the touch, seemed to have happened overnight after that lower than usual ph feed. I have checked for bugs also. Any thoughts?

 

Cheers mate. just surprised how quickly an off feed could affect them.

 

Only a T5 panel which is a good foot away.