You have a very serious problem there and those plants won't survive to harvest without attention.

Please DO NOT give advice when you don't know what you are talking about. You know who you are. If you don't I will be more than happy to point it out...

I'm moving this to 'problems' and calrifying the thread title.

There's a troubleshooting form at the top of the problems forums. Fill it out and we will see why the plants are curling under like that. One thing that I know already is that just an active intake is almost NEVER enough to give the sort of air exchange that cannabis requires. Standard setup is an active EXHAUST and a passive intake. You are going to want to change that, and add circulation fan(s) within the room to help with what appears at first glance to be suffocation from lack of air flow of the low leaves.