Yellow Stippling on leaf from interier to outward

I have a Diesel x Lowryder with some yellow stippling on the leaf interior. It starts near the stem of the leaf, and continues outward. See attach 200X pics...This has spread in the last few days to cover most of the bigger leaves on the entire plant. THis is an autoflowering plant, about 1.5-2 months old.
Growing indoors, with 2x600w HPS, 405cfm inline fan. I use pro-mix for my growing media/with bat guano added. My temps are at about 78 all the time, basement. No co2 supplementation.
Ive been using Greenfuse nutes at 1/2 strength, a drop of superthrive, with ph 5.5-6.0 water. I have yet to give this plant any Bloom nutes, i just put it into flower 4 days ago (from t5's). I also have several Cheese, and Alaskan Thunderfuck with no problems (same nutes used).
My first thought, I checked several leaves for spider mites, and found no signs of them.
Any input on this would be greatly appreciated...need more info? Let me know...

Can you give us a picture of the whole leaf, as well as maybe the plant? It's hard to say from those pictures.

now that its progressing the leaves are drying, and curling upward.

lights too close? too intense?

Looks like nute burn spreading thru the veins. Lowryders are more sensitive to nutes than a regular strain.