Curling Leaves

Hydroponic Skunk #11
Flowering Stage
What could these curling leaves mean?

I'm having a similar problem--I think it's heat related. The top of my tallest plant gets a little too close to the hps and gets heat related. From what I've read, these leaves are probably not going to recover. Just the way it is. Fortunately for me, its only the top few nodes experiencing the problem. Looks to be the case for you as well--the tips of your lower leaves look a little curled as well, so again heat stress.

Move your light a little higher or the plants a little farther way. Good luck.

thats a sure sign of overfert. heatstress has more of a tendency to cause leaves to curl upwards. I suspect your humidity levels may be on the very low side as well.