Pool Calcium Hardness Increase (Calcium Chloride)
Calcium chloride to raise a pool's calcium hardness -- the level that, with pH and alkalinity, sets the LSI balance (soft water corrodes plaster and metal, hard water scales). Hardness is expressed as CaCO3, so the dose converts the CaCO3-equivalent (ppm x gal x 8.34e-6 lb) to calcium chloride by the molecular-weight ratio 110.98/100.09 and divides by the product's calcium-chloride content: raising 20,000 gal by 20 ppm with 77% flake takes ~4.8 lb, or ~1.2 lb per 10,000 gal per 10 ppm (the shop rule of thumb); anhydrous (~94%) needs less. CAUTION: calcium chloride releases heat dissolving -- add it slowly to a bucket of water (never the reverse), pour in with the pump running, retest. Hardness only dilutes DOWN (drain and refill). A starting dose; the test kit, the target (typically 200-400 ppm), the product label, and CPO practice govern.
Formula and source
calcium_chloride_lb = ppm_increase x gallons x 8.34e-6 x (110.98/100.09) / (product_purity_pct/100); oz = lb x 16. The 110.98/100.09 converts CaCO3-equivalent hardness to lb of calcium chloride.
Pool calcium-hardness dosing with calcium chloride (mass balance with the CaCl2/CaCO3 molecular-weight conversion), by name; the test kit, the target hardness, the product label, and NSPF CPO practice govern.
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