leaf curling always over nute?

[fadetoblack1]

or can other problems cause it?

 

[Seamaiden]

Overwatering can also be a cause. Being too hot can look very similar.

 

[alpinehi]

Leaf curling/twisting is a general sign of stress. It could be a 100 different things. Checking the humidity and the things Sea mentioned is a good place to start.