Looks like Nute burn; I had a similar problem myself. I got nute burn then PH dropped and I got Nute Lockout. I flushed with clean PH adjusted water for 3-4 days. I then added nutes back in slowly and she started to get back in the groove of things. With nutes, less is more!!! Find your plants tolerance and stay close.

Look at new growth; the burnt leaves are burnt and wont get better. if the new leaves are not affected after the flush, you know whats the problems was.
cheers,

MJ