identify this plant problem

what is this? I am only just getting started and my main source of knowledge is the internet, not first hand. If I had to guess I would say nutrient burn. Anyone know?

It is happening on about 1 or 2 out of 10 of the leaves on 2 of my plants, and on only 1 or two leaves on the rest, all of which share a reservoir. They are under florescent only, and its not the top leaves (in most cases) so I am ruling out light burn, and the room is a constant 68 degrees.

do you smoke cigarettes or tobacco around your plants?

No Ricky, I do not.

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looks like a potassium deff to me buy this chart ive used throughout my grows

Nice chart.

yes, very helpful, how do I leave like, positive feedback, that deserves it.