To clarify, my Dad's issue is with a fiberglass hot tub. He has white rings forming just above the water line and is concerned about the heater getting fouled. His tap water is 1000 Calcium (from a well). When he called the spa manufacturer, they recommended a sequestering (also know as chelating?) agent such as Leisure Time Spa Defender. Am requesting MSDS sheets for it. They also suggested the ultimate solution would be to use 50% salt softener water with 50% well. My suggestion to him was to lower his pH from 8 to 7.4 and his alkalinity from 80 to 60. He uses bromine. Will look at the calculator you mention for langlier. Doesn't temp have a major influence on the scaling indices? Since the "surface temp" of a heater element is much higher than the surrounding water, doe this effect the optimum point to prevent scaling?
My other suggestion to him was that he may be better off just getting the water to where it won't form the white rings and not worry about the heater. It is supposedly S.S. Suggested he find out how difficult it is to remove and clean it since S.S. will easily tolerate acid cleaning.
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