fan leaves curling in?????

hi, my plants are about four weeks old and looking healthy, they are in canna soil under a 600w. when checking them today i noticed that the larger fan leaves are starting to curl in along the sides, does anybody know the reason for this???

Humidity is probably too low, mine do it all the time.
check out my albums, or post your pics and we will have a look cee

this has nothing to do with this post... but, I just wanna know how the hell to post my own topic?!?!!!

Pics would be nice, could be pH could be heat stress could be ventilation

yeah also how good is ventilation, get a fan gently blowing on them, that could cure the problem right there.