I agree with Rusty :thumbsup:

Nute burn will affect the edges of the leaves first. In this case, the plant just isn't using the fan leaves anymore, and I usually trim out the bottom of the canopy that is well shaded when this starts to happen. It is totally normal.

I also agree that adding side lighting will make a huge difference, you'll only get decent buds within a few inches of a fluro, so the more you add, the better.