While the experts come by to help you, Ill add that I've had those symptoms before, so maybe you can relate.
In my case it was either medium not properly mixed or something wrong at the root zone. I would use these organic powdered amendments that came in clumps and if i didn't make sure ALL the clumps were broken down well before mixing in the medium and evenly mixed with the rest of the ingredients, I'd get those symptoms.
Then I stopped using them because no mater how well i mixed and broke them down, i'd get at least one leaf with that symptom. For a while I didn't get the symptoms any more if i used very little of it, but they reapeared once when i began playing around with more watering. Never got them again once i changed into other amendments. Point being, you might have some "hot spots" of minerals in your medium.
Might be your case as well or not. But while you get a better diagnosis, I'd get some beneficials like Recharge or OG Biowar roots pack, just to make sure roots are getting microbes to help them be healthy. The tip of that big leaf on the second picture looks like symptoms i've seen several times of root rot begining. Does you runoff water have any smell?
