Ok well im going to say If you over water or under water they will do that same thing. Now what you need to do is find out if its over or under. then either let them dry out or water them. Ill show you a pic of my power skunk and this was do to over watering.
Um I did fix the problem but the leaves that wouldnt recoop I cut. I feed 7 plants 42 days into flower all together 3 gallons of water and I water 2-3 times a week 1 being nutes.