We sell spa sentry. it can be used in any condition of hardness. In any condition, it kicks the calcium out of solution, temporarily clouding the spa for about 1 day. The calcium is deposited in the filter, which you then removethe filter and rinse it out. The calcium is replaced by some sort of polymer. Your spa heater MUST be of during this 24 hour "calcium-kick-out" period. The product holds the ph for a month. Bormine tablet users see less than a month.