Free tool
Calcium Hardness Calculator
Calcium chloride to raise calcium hardness, an honest drain-and-refill calculation to lower it — no fabricated dosing math.
How to use this calculator
- 1Enter your pool volume
Don't know it? Use the Pool Volume Calculator first — this tool is built to work with that gallon figure.
- 2Choose raise or lower CH
Enter your current and target calcium hardness readings from a test kit or strip.
- 3Raising: read your calcium chloride dose
The calculator shows exactly how much calcium chloride to add, in pounds.
- 4Lowering: read your drain-and-refill amount
There's no chemical that lowers calcium hardness — the calculator instead shows how much water to drain and replace with fresh water to hit your target.
Frequently asked
Questions about calcium hardness
Why isn't there a chemical dose for lowering calcium hardness?
Because there genuinely isn't one — no chemical additive removes dissolved calcium from pool water. The only real fix is diluting it out with a partial drain-and-refill using lower-hardness water, or using a sequestering agent to keep existing calcium from depositing as visible scale (which manages the symptom, not the underlying number).
How does the drain-and-refill calculation work?
It's a simple mixing-ratio formula: your new calcium hardness equals your current reading times the fraction of water you keep, plus your fill water's hardness times the fraction you add back in. If you don't know your fill water's hardness, this calculator assumes close to 0 ppm, which is a reasonable estimate for most municipal tap water but will slightly overstate how much you need to drain.
What's the ideal calcium hardness range?
Most pool professionals target 200-400 ppm, with 150-400 ppm considered acceptable. Water that's too soft can etch plaster and grout over time; water that's too hard can deposit scale on surfaces, tile, and equipment.
What if I don't know my pool's exact volume?
Use the Pool Volume Calculator first to get a solid estimate, then come back here — the two tools are designed to work together.