I had a plant do that on the tips not quite that bad and it was only on a certain set of leaves. I decided what was causing my problem was me misting them with a weak nute. solution so I quit doing it and no problems. I would lighten up on the Nutes and see if it doesn't correct itself on new growth.
You thinking nutes burn so why not tell us what dirt and nutes you are and have used?
I would water with plain water back to back cause I don't like to flush.
But not knowing what you've fed and what dirt this is it's hard to say what to do for sure!
pic of the entire plant?
It could be nute burn, or it could be nothing. Like Ghetto said, just stop the nutes for a couple of waterings.
My plants are like that too and i havent used any nutes... i wouldnt worry about it as long as they are still growing and the tops look fine.