usually with lack of water they will curl down, basically they try to shade themselves more so the leaves evaporate less... No idea what causes them to turn up though. I had something kinda similar, though closer to what purplehazin posted, mostly on the new growth at the top. I was able to vent the temps down by 5-6 degrees to around 80, went super anal on water ph (as well as adding mag/cal/iron), and started covering the soil with sand to prevent fungus gnats, and it cleared up. No idea which of these things had the most effect, I kinda think all those issues were causing me a lot of separate problems.