Calcium Hardness Calculator
Calcium hardness (CH) protects plaster and equipment. Target range: 200–400 ppm for concrete/plaster pools; vinyl and fiberglass pools can run 150–250 ppm.
How the math works
- Dihydrate (77%): about 1.25 lbs per 10,000 gallons raises CH by 10 ppm
- Anhydride (94%+): about 1.0 lb per 10,000 gallons raises CH by 10 ppm
- Formula base: CH (lbs) = Δppm × Gallons × 8.34 ÷ 1,000,000 ÷ product strength
Before you add
- Dissolve granules in a bucket of water first, never straight into the pool — it generates heat.
- Pour the dissolved solution around the perimeter with the pump running, brush after.
- Low CH eats away at plaster and can corrode heater elements. High CH causes white scale on tiles and inside salt cells.
- Raising hardness and raising pH fight each other — adjust TA and pH after CH is set.
Frequently asked questions
How do I lower calcium hardness?
Same as CYA — only draining and refilling lowers it. Prevent scale by keeping pH on the lower side (7.2–7.4) while CH is high, and watch your salt cell for white scale buildup.
Is hard fill water a problem?
Check your tap water: many regions deliver 200–300 ppm CH. If your fill water is already 250, your pool will hover there naturally — just avoid pushing CH much above your fill water's baseline.
Can I use calcium chloride from the hardware store?
Yes — driveway "ice melt" calcium chloride is usually the same dihydrate compound. Avoid blends with salt or anti-caking additives; check the label says 77%+ calcium chloride.