Calculate how much calcium chloride to add to raise your pool's calcium hardness (CH) to target.
Calcium chloride releases heat as it dissolves (exothermic reaction). For increases over 25 ppm, split the dose over two days. Pre-dissolve in a bucket of pool water before broadcasting, and add with the pump running. Large undissolved piles can bleach vinyl liners or etch plaster.
Calcium hardness (CH) is how much dissolved calcium is in your pool water. It's one of the five factors in the Langelier Saturation Index (LSI) — the measure of whether your water is balanced, corrosive, or scaling.
Water with very low CH is aggressive: it wants to dissolve calcium from wherever it can find it — your pool plaster, grout, fittings, and equipment. This causes surface etching and pitting over time. Water with very high CH tips toward scaling, depositing calcium carbonate on surfaces, tile lines, and inside pipes.
Plaster (gunite): 200–400 ppm, ideally 250–350. Fiberglass: 150–250 ppm. Vinyl liner: 150–250 ppm. Concrete/pebble: 200–400 ppm. When in doubt, aim for 250–350 ppm — the middle of the safe range for most pool surfaces.
The standard calcium chloride dose formula:
lbs (77% CaCl₂) = (target CH − current CH) × pool gallons × 0.0000125
This is derived from the molecular weight of calcium (40.08 g/mol) relative to calcium chloride (110.98 g/mol), adjusted for 77% product purity and the weight of water (8.34 lbs/gallon). For 96% anhydrous calcium chloride, the dose is multiplied by 0.77/0.96 ≈ 0.80.
The 77% flake form (sold as pool calcium increaser, hardness increaser, or under brand names like Dow Flake) is the most widely available product at pool supply stores. Anhydrous 96% is more concentrated and sometimes available in bulk.
A 15,000-gallon pool tests at 120 ppm CH. The target for a plaster pool is 300 ppm — an increase of 180 ppm.
Dose = 180 × 15,000 × 0.0000125 = 33.75 lbs of 77% calcium chloride. Split into three additions of roughly 11 lbs each on consecutive days, with the pump running. Retest before each addition to confirm the previous dose has fully dissolved and circulated.
For plaster and gunite pools: 250–350 ppm is the sweet spot. For fiberglass and vinyl liner pools: 150–250 ppm — lower is acceptable because these surfaces don't leach calcium the way plaster does. CH also affects your LSI score along with pH, alkalinity, and temperature, so use the LSI calculator to check the full picture.
Yes, but pre-dissolving in a bucket first is safer for vinyl liners and reduces the risk of a localized hot spot on plaster. If broadcasting dry, spread it evenly across the pool surface — never dump it in one spot — and keep the pump running to circulate it. The product will dissolve within a few hours.
For increases under 25 ppm, a single addition is fine. For larger increases, split the dose over multiple days and retest between additions. This prevents temporary clouding from calcium carbonate precipitation, and ensures you don't overshoot your target — there's no chemical way to lower CH once it's too high.
CH above 400–500 ppm causes scaling: white, chalky deposits on pool surfaces, tile lines, the waterline, and inside the filter and heater. It also forces LSI positive, accelerating calcium carbonate precipitation. The only correction is dilution — drain a portion of your pool and refill with fresh water. Test your fill water's hardness first, since tap water in some areas already has high CH.
Dissolved calcium ions are stable in water and won't bond to a product that removes them from solution. Sequestering agents and scale inhibitors can prevent calcium from precipitating out, but they leave the CH reading unchanged. To lower CH, you must replace some of the pool water with water that has lower calcium content.
PoolChem Tracker logs calcium hardness alongside pH, alkalinity, and temperature — then calculates your LSI score and tells you exactly what to adjust.
