stain and scale control, metal gone, etc.
A certain amount of hard water is good for the spa, UP TO 150PPM, too hard and water can cloud because hot water does not hold calcium like cool water.
Iron and copper will also be chelated by the stain and scale control. if staining in bathtub, sinks, or dishwasher is present, use 1/4 cup stain and scale on initial fill, then use a maintenance dose once per week. no shocking for 24 hrs. on initial fill.