I'm no expert by any stretch of the imagination, and I'm still trying to develop a better understanding of plant problems and symptoms. But if I were to guess what's happening with your plant with no real information about your grow, I see the tips and edges look burnt, which makes me suspect that you've possiby overfed and caused a lockout of some sort. If it were me, I'd probably flush and then try giving a low dose of nutrients, and keep a close eye on new growth.
But again, I'm no expert and I could be way off here. Hopefully someone more knowledgeable than I am will have an opinion. That's just the first thing I thought of when I saw your picture.
Good luck.