Tips Curling, This heat or????

I read tips curling and drying out is from heat but also caused by a few other things, can anyone maybe pin point what is causing this?
5 out of 15 plants have this.... all in same room, 600watt MH 2ft above with glass, it doesn't feel hot above plant what so ever.

Got a fan?
What's temps?
You want answers, we need info.

Any other opinions?

DEA lab created plant aids/cancer. Resistant bacterial,fungus,blight,rust,pythium blend. Give it a cycle or two and they'll all have it.

2 more plants picked up the curling leafs up top.......

Well IMO you either sprayed them with the lights on (that's what the spots on the leaves look like), or you have a leaf muncher in there somewhere, and try to keep the temps around 70-75 and about 40% humidity...and no the leaves won't heal, look for new healthy growth and go with it...g/l