Plant leave curling help

I have a plant that 's in veg under T5 lights 18hrs on 6hrs off and few of the leaves side is curling up

possibility of heat stress

That's what I was thinking but it's under T5 light.

combination of low humidity and a fan

Does look like heat stress, but cant be if theyre inder cfl's. Unless your space is just crazy hot. The only other thing I can think of would be low humidity like rl420 said..in low humidity situations plants will close their stomata in an effort to conserve water. Sometimes it results in leaf curling..wish I knew more on the subject but hope this helps? haha
Happy growing!

Mine curl too but very differently? Those look like they were hot and dry, based on just general leaf knowledge. I'm a newbie.

I'm vegging them in my patio but there's air's coming in and out but I'm not sure if I need a fan and out of 12 clones this is the only one that's curling up.