First thing mate is to get a diary going. From there I/we can get information straight away that would help to diagnose.
The problem is from an over feeding. When the strength is too high that is the first sign. Roots too are getting burned.
Best thing is to flush and reintroduce a lower strength feed. But there are lots of variables like age, growing media, nutrients etc.
Autos generally don't need as much.
You look to be quite far on so I'd just start to flush now anyway.