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.
Frequently asked questions
Water low in calcium is aggressive and pulls calcium back out of whatever it touches. That means etching of your plaster, grout, and equipment as the water tries to satisfy its calcium demand from the surfaces around it.
Most Florida municipal fill water already comes in at 250 to 500 ppm, at or above the upper target. Every time you top off after evaporation you concentrate the calcium further, so an untreated Florida pool can climb past 700 ppm over a year.
About 1.5 pounds of calcium chloride raises calcium hardness by roughly 10 ppm in a 10,000-gallon pool. Scale the dose to your pool volume and the gap between your current reading and your target range.
No. Calcium reducers chelate the calcium so it hides from your test, but they don't remove it from the water. The calcium comes back. The only reliable ways to lower it are diluting with low-calcium water or reverse-osmosis service.
Calcium hardness is one of five variables in the Langelier Saturation Index, which predicts whether water will scale or etch. Keeping the LSI between -0.3 and +0.3 matters more than any single reading, so calcium is judged in context, not alone.
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