Raised Leaf Edges?

Some of the leaves on my plants are starting to raise right at the edges. This is my first grow so I'm not really sure what's causing it, or if it might just be a genetic trait.

I thought maybe heat stress, but it stays right in the mid 70's at the canopy at about 50% humidity.

They're sitting under a 600w HPS a little over 2' over canopy. I only use PH'd tap water with fox farm grow big at 1/4 strength.

Any ideas would be awesome

Yeah, mine kinda crisp up at the edges too, but she seems to be doing fine. I'd like an answer too, just to know nothing is going wrong.

You thinking it isn't heat stress, really is.
George Cervantes said it best: "When leaves start to become canoe like, back off the light".
Your temps sound great, but maybe the height ratio of your 600 is too close.
Back it off for a couple hours and see if the problem doesn't fix itself.