Calcium hardness (CH) measures how much dissolved calcium is in your water. Too little and the water will pull calcium out of your plaster, grout, and equipment (etching). Too much and calcium precipitates out as scale on tile, salt cells, and heater elements.
Target ranges:
- Plaster/concrete pools: 200–400 ppm
- Vinyl liner pools: 150–250 ppm
- Fiberglass pools: 150–250 ppm
Florida's calcium problem
Most Florida municipal fill water comes in at 250–500 ppm calcium hardness. That's already at or above the upper target. Every time you top off from evaporation, you concentrate the calcium further. Over a year, an untreated Florida pool can climb to 700+ ppm.
How to raise calcium hardness
Add calcium chloride. 1.5 lb raises CH by ~10 ppm in a 10,000-gallon pool.
How to lower calcium hardness
Only two options:
- Dilute with low-CH water. Partial drain and refill. If your fill water is hard too, this only helps so much.
- Reverse osmosis service. The only reliable way to reduce CH in Florida.
Don't fall for “calcium reducer” products. They chelate the calcium (hide it from tests) but don't remove it. It'll come back.
The LSI connection
Calcium hardness is one of five variables in the Langelier Saturation Index, which predicts whether water will scale or etch. Keeping LSI between -0.3 and +0.3 matters more than any single parameter — see our LSI guide for the math.