more info...what do you mean curl????could be to hot,to dry ,sick,overfert,ect.do they curl up?curl down?color change?
do they have necrotic patches on the tips of the leaves? does it only appear on the lower half....top....or middle?
browning or burning.you need to really give a good discription of every thing your doing to the plants,light distance,heat in the room watering schedual,how often you fertilize.if there browning and curling up it sounds like you over fertilized them.they may just be too dry(if in dirt)alot of things could be going wrong...they curl...they curl up is just not enough to know what your dealing with...we need varibles to work with.
lol i had plants that the bottom part of the plant was curling this however turned out to be under fertalization. so once again........give us some details