You over nuted probably too early in the life cycle. The toasted leaves are the lower leaves, followed by lots of leaves with burnt tips which are typical of over nuting. As the plant has grown, the tips are looking better at each level. My guess is that you had a self induced problem that is working its way out. The little bugger is real resilient . Be careful when nuting the wee ones. Even a little too soon can bite you in the butt. Check out the threads on when, and how much to nute the babies. I never nute before the third set of leaves unless the cotes pale and tell me it is time. Most of your plant looks better than some I have seen grown by nute pushers. Don't worry, just pay attention to what the plant tells you. Good luck. Peace & be kind.