In the house we just bought the master bath has a whirlpool bathtub. When we start it a small amount of brownish/blackish stuff comes out. The house inspector said this is normal because the water gets in the jets and stays when you shut it off. I want to get it clean so I don't feel as if we are bathing with gunk in the water. I have tried running it with bleach mixed with the water. That didn't help much. What can I do to get these clean?