What are the different causes of leaves curling downward aka the claw?

I know different things can cause this but what are the most common?

heat stress can cause curling/twisting downwards

Thanks I posted on this before in complete detail and none would answer. I think it happened when i switched from cfls to mh light . i tryed it without the glass and it was too hot .I got the glass in it now and am venting with a 4 in can fan .

Yeah npk test shows nitrogen is high and other two are low.But branch sets above it are fine . And yeah not enough drainage i,m gonna use more perlite next grow.Unless someone knows some tips on improving it throughout this grow.

Yeah, the claw is usually associated with Nitrogen overdose, although the claw you have in your picture is more droopy than the normal N-overdose claw. It is probably due to not having enough drainage and overwatering.

If you prepare a new pot with good soil and more perlite, you can transplant your plant into it and that will help a lot with drainage.

Hello everyone Im a noobie to the forum. I have the same problem and Im 3 weeks into flower. What can i do about this problem. I tried flushing. I was wondering if there was something else I could do. Any advise would be appreciated. Regards. also will your floweres mature with this problem.