Magnesium nutrient lock out, triggered by too much potassium ?

Good morning, I'd say the leaf symptoms are definitely looking like a magnesium deficiency , fortunately you caught it before it started getting a lot of brown spots and progressing further up the plant. After doing your few foliar applications you might want to add some dolomite lime to the soil so it can have a steady supply over time. Just be mindful that lime products will raise the soil ph slightly. Otherwise you can always use the Epsom salt for watering the soil periodically as well. I can't say if it was the potassium lockout, or possibly the ph is off. If you continue to see more leaf troubles you might want to consider checking the runoff ph to verify it's in the right range. Good luck with the rest of the grow.✌️