Healthy looking plants, but leaf edges are turned up

High there, I'm growing Double Dutch at the moment under a 600w hps, they are 2 and a half weeks old, and apart from the leaves turning up at the edges they seem to be growing well. It's not an over fertalizer problem as I've not used any and the leaves are a healthy green colour all over so it's not leaf burn. It doesn't seem to be a problem yet but prevention is the best cure.

Any help would be much appreciated, cheers

HEAT baby.. HEAT... its to fucking hot in here... open a window.... leaves up mean to much heat... turn the fan on I'm dying..... lol

am I right?