Calcium Hardness Calculator
Enter your pool volume, current/target CH, and your product's purity — we'll calculate the dose.
Result
Enter your numbers above to see the result.
Safety first
- Never mix chemicals together.
- Always add the chemical to the water — never water to the chemical.
- Wear gloves and eye protection when handling pool/spa chemicals.
- Keep chemicals out of reach of children and pets.
- Always follow the product label — it overrides any guidance here.
Ideal CH range
250-400 ppm (plaster), 150-250 ppm (vinyl/fiberglass or hot tubs).
Frequently asked questions
Why does calcium hardness (CH) matter?
Too low, and your water becomes aggressive — it will pull calcium out of plaster, grout, and metal fittings (corrosive). Too high, and calcium can precipitate out as scale on surfaces and in your heater.
What CH range should I target?
250-400 ppm for plaster/gunite pools, 150-250 ppm for vinyl or fiberglass pools, and 150-250 ppm for hot tubs.
What product do I use, and what purity should I enter?
Calcium chloride is the standard product — check the label for its purity (often 77-80% or 94-97%) and enter that here for an accurate dose.
How do I lower calcium hardness?
The only way is dilution — replace part of your pool water with fresh, lower-calcium water.