Calcium Hardness
The concentration of dissolved calcium in pool water, affecting scaling and corrosion tendency.
Definition
Calcium hardness (CH) is the measure of dissolved calcium ions in pool water. It is one of the five variables in the Langelier Saturation Index. Water with low calcium is aggressive — it will dissolve calcium from plaster, grout, and equipment. Water with high calcium is scale-forming — calcium carbonate precipitates on surfaces and inside equipment. The ideal range depends on pool surface type: plaster pools need higher calcium (200–400 ppm) than vinyl or fiberglass pools (150–250 ppm). Calcium hardness can only be lowered through partial drain and refill.
Quick Facts
- Ideal Range
- 200–400 ppm
- Units
- ppm
- Also Known As
- CH, calcium hardness, calcium, water hardness, hardness
Relationships
Outgoing Relationships
- measured by → Water Testing
- part of → Langelier Saturation Index
- explained by → glossary/calcium-hardness
- causes → Scaling
- causes → Corrosion
- requires → Calcium Chloride
- recommended for → Concrete Pool
Incoming Relationships
- measured by ← Langelier Saturation Index
- requires ← Water Balancing
- requires ← Concrete Pool
- related to ← Vinyl Pool
- related to ← Fiberglass Pool
- references ← PHTA