Calcium hardness is a measure of the water’s calcium content and, therefore, relates to the water’s corrosive tendencies. Too much calcium in the water causes it to precipitate out of the water and leads to deposits on sur- > faces and piping. Too little calcium leads to corrosion and etching.
The ideal range for calcium hardness for spas is 150 to 250 ppm, though some manufacturers may recommend a narrower range, depending on the type of spa shell you have.
Testing Calcium Hardness. You’ll need a liquid test kit to monitor the level.
Adjusting Calcium Hardness. Low calcium hardness tends to be a more common problem than high calcium hardness. To raise the level, carefully add predissolved calcium chloride. In the rare instance that the level is too high, replace some of the pool or spa water with fresh water.