Pool Calcium Hardness Calculator

Protecting plaster and equipment

Calcium hardness measures dissolved calcium in pool water - too little makes water aggressive toward plaster, grout, and metal fittings (drawing calcium out of surfaces to compensate), while too much risks visible scale buildup on tile lines and equipment.

Worked example

For a 20,000-gallon pool at 150 ppm calcium hardness, targeting 250 ppm:

Dose = (20000/10000) x ((250-150)/10) x 1.25 = 25.0 lbs calcium chloride

Frequently asked questions

What is a good target range? Most plaster pools are recommended to stay between 200-400 ppm calcium hardness, while vinyl and fiberglass pools (less sensitive to low hardness since there's no plaster to protect) can often run somewhat lower.

Can calcium hardness be lowered chemically? No - like cyanuric acid, excess calcium hardness cannot be removed chemically. The only way to lower it is partial water replacement with fresh water containing less calcium.