I'm not sure about bath salts. I have heard conflicting things on them. I would call your Dr on that one really quick.
As far as the temperature. I was told that if the water is too hot for you to put your foot in without having to ease it in, then it is too hot to sit in. Also, if the water starts to turn your skin pink, then it is too hot. The good thing about baths, is the water cools gradually, so you can stay in them longer/have them a bit warmer than you could with a shower.