Hey Rusty, look it up online. It looks very similar to this burn, but it has a mold that can be seen on the bottom of the leaf. I was told over and over that was my problem, turns out, I was creating a K deficiency with my rare nute additions. I added back in K and the problem stops, damage cannot be reversed. First sign is the red goes beyond the petiole and into the main leaf veins.

I like some stuff called Ultra Snowstorm to give the K