I had my pool closed on 10/31 and today I opened the cover just to see what's going on in there and I noticed a white powdery substance on the bottom of the hot tub and some in the pool as well. The water is very cold as we're having a really cold winter so far (although it was 60F today and its gonna be 70F tomorrow). Is it possible that one of the chemicals has precipitated out since the water is so cold, is it something I have to worry about? I'll get pictures posted tomorrow.