Calcium Hardness Calculator
Calculate how much calcium chloride to add to raise your pool calcium hardness (CH).
CALCIUM CALC
Calcium Hardness Adjustment
Quick-pick — auto-fills volume below.
Recommended: 250-400 ppm for plaster pools
Calcium Chloride Dosage
-- lbs
Calcium chloride to add
Also equals
-- oz
Will raise CH to
-- ppm
Assumes flake/dihydrate calcium chloride (~77–80%), the common pool product. If yours is anhydrous (94%+), add about 20–25% less.
Buy Calcium Chloride on Amazon
How to Add Calcium Chloride:
- Pre-dissolve in a bucket of pool water (never add dry)
- Add slowly in front of a return jet
- Wait 24 hours before retesting
- Don't add more than 10 lbs per 10,000 gallons at once
What is Calcium Hardness?
Calcium Hardness (CH) measures the dissolved calcium in your pool water. Too low = water becomes aggressive and attacks plaster, grout, and equipment. Too high = scale buildup and cloudy water.
Target CH by Pool Type
| Pool Surface | Target CH | Minimum |
|---|---|---|
| Plaster / Gunite | 300-400 ppm | 250 ppm |
| Pebble / Aggregate | 300-400 ppm | 250 ppm |
| Vinyl Liner | ~200 ppm common target | TFP/PoolMath: 50-550 target, 0-650 safe |
| Fiberglass | 150-250 ppm (no surface need) | ~150 w/ heater |
CH Too Low?
- Water etches/dissolves plaster (looks rough, pitted)
- Grout and tile deterioration
- Metal corrosion (heater, ladder, pump)
- Vinyl & fiberglass surfaces are not harmed by low CH — there the only low-CH concern is metal equipment (above)
CH Too High?
- Scale buildup on tile line
- Cloudy water
- Scale in heater (reduces efficiency)
- Salt cell scaling (SWG pools)
Lowering Calcium Hardness:
You can't chemically remove calcium. The only solution is to drain and refill with softer water, or use a reverse osmosis water treatment service.
You can't chemically remove calcium. The only solution is to drain and refill with softer water, or use a reverse osmosis water treatment service.
Calcium Hardness & LSI
Calcium Hardness is a key component of the Langelier Saturation Index (LSI), which measures water balance. For plaster pools, maintaining proper CH is critical to prevent etching.
| LSI Value | Water Condition |
|---|---|
| Below -0.3 | Corrosive / Aggressive (attacks plaster) |
| -0.3 to +0.3 | Balanced (ideal) |
| Above +0.3 | Scale forming |
For educational purposes only — full disclaimer ↓