Looks to me like a PH problem caused by too much nutrients building up in the soil. This creates hot spots. Too much of a fluctuation.
It may be possible that some nutrients have been locked out. I thought I could see some other plants leaves curling inwards too.

Also, what is your humidity ? Is it very dry in there ?

Anyway, I would back off with the nutrients and give the plant a very good flush with distilled water if you have it. How accurate is your PH reading ?
Take another PH reading, correct it and see how it behaves over the next week.

good luck with it.
silent leprechaun Reviewed by silent leprechaun on . What IS This? 284557284558284559 I have 10 girls, 9 of which are pretty similar with 1 being totally different. It is this one odd plant that i am worried about. This particular plant was different from the start. She ha much skinner leaves and is more bushy than tall, with many spidery branches. In the past few days, her leaves have started to really curl up - curl down, I should say - and the sides of the leaves are also curling in and down, towards the leaf midvein. (See Pic 1). The other 9 Rating: 5