The best advice I ever got from the "old-timers" is <WHEN IN DOUBT, DO A WATER CHANGE> Clamped fins is the first sign of stress in many sp. of fish. This may be from a disease or pathogen, or stress from a sudden change or prolonged exposure to unfavorable water parameters.
I'd suggest a 25% WC, repeated in a couple of days. If there are signs of ich, dose accordingly with quick cure. Adding rock salt is old school, but IME it still works. 2 Tbs for a 10 gal...
Where do you live? It's been chilly at night, here in Mililani but I hardly think it would be too cold for your fish at night. I keep almost all my fish outdoors and none are stressing over the cold. (including some Loricariides that break out in ich when they get too chilled) In fact, according to some of my cool water killies, this winter has been a mild one for us as they did not give me a single egg this winter

cause it did not get cold enough.