Quote Originally Posted by cwesto
Any other possibilities???
There are lots of possibilities, bro. It's difficult to tell without pictures, knowing whether you're growing in soil or hydro, etc.

Again, unstable pH fluctuations, salt buildup, nutrient lockout...these can all result in leaf curl. So can deficiencies of Magnesium and Phosphorus. If it's an excess nutrient problem or salt buildup, a good flush should help. Followed by a light (1/4 strength) feed.

Also, even though the ambient temperature in the room is reasonable, the tops of the plants can get too hot if growing too close to the light. Try upping your ventilation around the light, bend the tops away from the light, or just raise the light itself.