15,000 gallon IG plaster

Alkalinity here is naturally high out of the tap, pool tested at 220ppm. Their test said pH was 8.2, all mine say it's closer to 7.6.

Their advice: 1/6 cup muriatic acid in the water for one hour without the pump running then run pump for 23 hours, repeat, repeat. (Three days total)

Hardness is also naturally high, but a disproportionate amount is magnesium, almost a 2:1 ratio of calcium:magnesium when most waters are 3:1 or 4:1.

I don't see any scaling problems, so I'm not particularly worried about the alkalinity, but I am curious about the suggested method - anyone hear of this one?