Strange Leaf Blight - Grey Blotches

My plants have some sort of plant disease I believe. My leaves show blotches that progressively get worse - pics attached. I have researched from good and thorough sources and cannot find the cause of this particular leaf symptom. The leaves start off with only a few blotches (which are kind of a greyish color and get worse covering most of the outer parts of the leaf before it dies and dries up. Strangely the disease effects only the lower half of the plant, which made me think of root disease but I looked into the possibility of Pythium thoroughly and I'm sure it is not that. What other root diseases could cause this type of leaf symptom?
I have sprayed with Neem oil and it has no effect.

My setup is as follows:
Flood and drain system with a 100 gallon res and 4 x 8 tray. Medium is coco coir in 3 gallon "smart pots". I water twice a day during light cycle only of course. There is plenty of fan movement in the room and temp usually stays between 72 and 78 but sometime goes to as high as 84. RH is usually around 45 but has climbed to as high as 60.

This problem is definitely affecting yield. I am desperate to figure this out so any help will be greatly appreciated.