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When you say disinfected the tub - did you put a lot (100 PMM chlorine) into the tub? If you let the water get away from you, maybe it needs a lot of chlorine to clean it out. Sometimes people use a "shock value" of 10 PPM chlorine and think it's good. Doc has a paragraph under the FAQ section about this type of disinfection.Did you try switching your sanitizer?Go to Doc's site - I believe he sells Spa Magic and he has some blurbs on it. Also, some people there use "The Natural" that he sells and swear by it.Good Luck!