usually, when the leaves curl up liek that its because of heat stress
when they are too hot they will do that.
also looks liek those curled leaves are dried out too....did you forget to water
what size hid r u using??
if you were using a 400 or somethin and had it too close you would heat them up too much.
if your humidity is that low, you need to get it up.....
depending on your grow spot size, get a bowl or bucket and fill it with water....it will help raise humidity
also depending on ur temps turn the exhaust down so that you can let the room have a bit higher humidity