without knowing your growing medium and pattern its hard to help.

Drooping is caused by several things, some of which have been pointed out already, PH, oxygen, etc. One thing that hasn't been pointed out is that some drooping is natural as the plant gets older in the season.

I would get in your medium and check things out since you just started 12/12 cycles. And if everything seems to be on point, give them a little superthrive and they should be just fine.