Today I came home an ran a bath, the water started clear then turned cloudy. I thought the bathtub could be dirty so I cleaned it. But when I ran new water it was still dirty. At first it was just the cold water that was dirty,beacasuse I tried runnning one at a time, but after about a minute the hot water was turning dirty too. It doesn't leave soot or a film in the tub, what could cause this?