About this tool
The Calcium Hardness Increaser Calculator is a free, in-browser tool that computes how much calcium chloride to add to raise a pool's calcium hardness (CH) to your target. Calcium hardness is a key part of water balance and the Langelier Saturation Index (LSI): too low and the water becomes corrosive, etching plaster and gunite surfaces; too high and scale forms. The ideal range is roughly 200–400 ppm. All arithmetic runs locally in your browser, so nothing you enter is uploaded.
The method converts gallons to liters (L = gallons × 3.78541) and finds the CaCO₃-equivalent mass needed: CaCO₃eq grams = delta_ppm × L / 1000. Because calcium chloride is heavier per unit of calcium than calcium carbonate, the product mass is CaCO₃eq × (MW / 100.09) ÷ purity, where the molar mass MW is 110.98 for anhydrous CaCl₂ or 147.01 for calcium chloride dihydrate (CaCl₂·2H₂O), and purity is entered as a percentage (for example 77% flake). Results are shown in grams, ounces, pounds, and kilograms.
As a check on the numbers, 100%-pure anhydrous calcium chloride works out to about 0.93 lb per 10,000 gallons to raise CH by 10 ppm. Note that this tool only raises hardness — calcium hardness cannot be lowered chemically; it comes down only by partially draining and refilling with softer water. Add calcium chloride to a bucket of water (it releases heat), broadcast with the pump running, and re-test after it circulates.