You're running REAL chilly and your day/night swing, especially in the 'hot spot' could be not only causing physical stress to teh upper leaves, but also creating conditions for dewfall when the lights go out and the resulting fungal diseases that damp plants are prone to. Also if your bags are on a cold cement floor you have GOT to lift them up to keep the soil from getting that cold- cold wet soil that is acidic will kill plants!!! Get your night minimum temps up to 65'F, and yup you need to get your air flow back where it was before the problem. I think you are seeing a set if environmental factors working together to create this problem. I'd pick up some Serenade too and do a light mist right at lights-on with it. It's an organic live-culture fungicide that is safe for flowering plants.