How to raise calcium hardness in a pool The short answer To raise calcium hardness in a pool, add calcium chloride (sold as “Calcium Hardness Increaser”): about 1.2 lb of the 77% kind raises 10,000 gallons by 10 ppm. Dissolve it in a bucket of pool water first — it gets hot — and pour it around the pool with the pump running. Aim for 250–450 ppm with plaster, 150–350 ppm with vinyl or fiberglass.
How much calcium your pool needs Calcium now
Calcium hardness. Too little eats plaster and heaters; too much leaves white scale.
Calcium you want
Good range: 250–450 ppm.
Type the size and your calcium reading.
Step by step Work out the dose with the calculator on this page, for the calcium chloride you have (77% or 94%).
Dissolve it in a bucket of pool water — add the calcium to the water, and expect the bucket to get warm.
Pour it around the pool with the pump running. A big dose goes in parts.
The product label always wins — if it says something different, follow the label.
Why it happens Soft fill water (rain, some towns’ water) starts calcium low, and water that is low in calcium dissolves it out of plaster and grout.
Questions What if calcium hardness is too high? Nothing takes it out: replace some of the water with fresh, softer water.
Does a vinyl pool need calcium? Less: 150–350 ppm is fine. It still protects metal parts and heaters.
77% or 94% calcium chloride? The 94% kind is stronger, so you need a bit less. The calculator handles both.
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