How the calcium chloride dose is worked out
lb = (target − current) ÷ 10 × 1.25 × gallons ÷ 10,000 (77 %) · × 1.0 for 94 %
Calcium hardness is measured as ppm of calcium carbonate. Raising 10,000 gallons (about 83,450 lb of water) by 10 ppm takes 0.83 lb of calcium carbonate equivalent, which is 0.93 lb of pure calcium chloride: about 1.0 lb of the 94 % anhydrous product and 1.2 to 1.25 lb of the 77 % dihydrate flakes. A 10,000-gallon pool from 200 to 300 ppm needs 12.5 lb of flakes or 10 lb of pellets; a 20,000-gallon pool from 150 to 250 ppm needs 25 lb of flakes.
Add it in portions: dissolve each portion in a bucket of pool water (calcium into water, never water onto the calcium), pour it around the deep end with the pump running, and retest after a full turnover before the next one.
What level to aim for
Many guides aim for 200 to 400 ppm in plaster, pebble and tile pools, where low calcium slowly etches the surface; vinyl and fiberglass pools are often run lower. The level works together with pH, alkalinity and temperature, so balance those as well: the pool pH calculator and the pool alkalinity calculator do the doses. Cal-hypo shock adds a little calcium with every use. Calcium only leaves the water when you drain it, so the fix for too much is replacing part of the water; the fill time calculator tells you how long the refill takes.
Dose factors worked out from the molar masses of calcium carbonate (100.09) and calcium chloride (110.98) and cross-checked with product labels (1 lb of 100 % calcium chloride per 10 ppm per 10,000 gallons). Read October 23, 2026.
Frequently asked questions
How much calcium chloride do I need to raise calcium hardness?
In 10,000 gallons, 1.25 lb of 77 % calcium chloride flakes or 1.0 lb of 94 % pellets raises calcium hardness by 10 ppm. Going from 200 to 300 ppm takes 12.5 lb of flakes or 10 lb of pellets; twice the gallons, twice the amount.
How much calcium hardness increaser for a 15,000 gallon pool?
About 1.9 lb of 77 % calcium chloride per 10 ppm, or 1.5 lb of 94 %. From 150 to 250 ppm that is 18.75 lb of flakes or 15 lb of pellets. Add it in two or three portions and retest between them.
What should calcium hardness be in a pool?
Many guides aim for 200 to 400 ppm in plaster, pebble and tile pools, where soft water slowly etches the surface; vinyl and fiberglass pools are often kept lower. The right level also depends on pH, alkalinity and water temperature, so balance those together.
How do you lower calcium hardness in a pool?
By replacing part of the water with softer fill water; no common pool chemical removes calcium. Going from 500 to 350 ppm with soft fill water means replacing about 30 % of the water. Test your tap water first, since hard tap water lowers it less.
Can I add calcium chloride directly to the pool?
Dissolve it first: add the calcium chloride to a bucket of pool water, never water onto the calcium, because it heats up a lot. Pour it around the deep end with the pump running, and add large doses in portions so the water does not cloud.