I wouldnt go chasing to many problems yet. The plant looks pretty healty overall.
Hmm, I have to say that I wouldn't freak too much right now. Looks to me like you're probably having a little fluke in the plant.
I think that once you start getting troubles on more than one leaf, that's when you would be facing a systemic problem.
If you're worried about nute burn (which I'm not convinced it is), you can always flush things out and see what happens.
But the plants do seem to be healthy overall - and just a few leafs with some troubles can be removed.
Take em off, if there are only a few, then see what happens.
Breathe, breathe....