Calcium Hardness Calculator
Enter your pool volume and current and target calcium hardness to get exactly how much calcium chloride to add, for dihydrate flake or anhydrous. The dosing comes from the standard mass balance, cross-checked against established pool-chemistry sources.
Calcium chloride to raise CH by 100 ppm
18.4 lb
294.5 oz
of calcium chloride (dihydrate)
Aim for 200 to 400 ppm in plaster or concrete pools and 150 to 250 ppm in vinyl or fiberglass pools. Calcium chloride gives off heat as it dissolves, so add it to a bucket of water (never water to chemical), pour it around the perimeter with the pump running, and retest after a few hours. The dihydrate flake form is what most pool hardness increasers use.
Why calcium hardness matters
Water wants calcium. If your calcium hardness is too low, the water pulls it from plaster, grout, and metal, etching surfaces and corroding equipment. Too high, and it drops out as cloudy water and scale on tile and the heater. Keeping it in range, along with pH and alkalinity, is what the saturation index is really about. Start from an accurate pool volume, and balance the rest with the alkalinity calculator and the full calculator list.
Frequently asked questions
How much calcium chloride raises hardness?
About 1.25 pounds of dihydrate calcium chloride per 10,000 gallons raises calcium hardness by roughly 10 ppm. Anhydrous calcium chloride is more concentrated, so it takes about 0.9 pounds for the same change. This calculator handles both.
What should pool calcium hardness be?
Aim for 200 to 400 ppm in plaster or concrete pools, where calcium protects the surface, and 150 to 250 ppm in vinyl or fiberglass pools. Too low can be corrosive and etch plaster; too high causes cloudy water and scale.
How do I lower calcium hardness?
You cannot lower it with chemicals. The only reliable way is to drain part of the pool and refill with water that has lower calcium. If your fill water is hard, that is the usual reason hardness creeps up over time.
What is the difference between dihydrate and anhydrous calcium chloride?
Dihydrate calcium chloride contains water of crystallization and is the flake form most pool hardness increasers use. Anhydrous calcium chloride has no water, so it is more concentrated and you use less of it. Pick the type you actually have, because the dose differs.
Why does calcium chloride get hot?
Dissolving calcium chloride is exothermic, meaning it releases heat. Always add it to a bucket of water rather than water to the chemical, pour it around the pool perimeter with the pump running, and never breathe the dust.
Dosing from the standard mass balance: about 1.23 lb dihydrate or 0.93 lb anhydrous calcium chloride per 10,000 gallons per 10 ppm, consistent with the 1.2 to 1.25 lb dihydrate figure from established pool-chemistry references. Follow your product label and retest.