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Calcium in a modern acrylic spa is not as important as in the past. Calcium lightly coats the metal parts of a spa and helps prevent corrosion. Todays spas are built of materials that are much more resistant.
Thanks for the replies. The link zzaphod42 posted in his reply, interestingly enough, is hosted by my dealer's website, Central Jersey Pools. I should have followed my instincts when I filled my spa for the first time, but I didn't figure trying the stuff the dealer sent along with my spa would do any harm. I can't imagine that running that Simplex garbage in my spa for only 4 weeks or so could have done any real damage to my spa, though.
I noticed a few people mention "Spa Defender" in their posts. I use a product called "Minquest" which is a stain and scale remover. Is this basically an identical product, or do I need to use "Spa Defender" in addition to, or in place of the "Minquest" I already use.
Minquest is a powerfully concentrated and effective metal, stain, and scale reducer/eliminator which inhibits the formation of rusty, green, brown, black or cloudy precipitates in spa water. It can also be added to clear up metal coloration already present in your spa water. Unlike products such as Metal Gon™ which require adding the entire bottle, Minquest is concentrated and very economical to use, requiring only 3 oz. per 500 gallons!