What is Calcium Hardness?
Calcium hardness (CH) is a measure of the amount of dissolved calcium and magnesium minerals in your pool water, expressed in parts per million (ppm). It is a critical component of overall water balance, working alongside pH and alkalinity to ensure the water is not corrosive or scale-forming. When calcium levels are properly balanced, the water is considered to be in a state of equilibrium. Without enough calcium, the water becomes aggressive and actively seeks to dissolve it from any available source, such as the pool's plaster or grout. Conversely, too much calcium can lead to it precipitating out of solution and forming unsightly scale.
Normal Calcium Hardness Levels by Pool Surface
For different pool surfaces, the ideal calcium hardness range can vary significantly. This is because certain materials, like plaster and concrete, are made with calcium and need a higher concentration in the water to prevent leaching. In contrast, surfaces like vinyl and fiberglass do not have a calcium source to pull from, so they require a lower range. Maintaining the specific target for your pool's surface is key to preventing long-term damage.
Comparison Table: Ideal CH Levels
| Pool Surface | Recommended Calcium Hardness Level (ppm) |
|---|---|
| Concrete or Plaster | 200–275 ppm |
| Vinyl or Fiberglass | 175–225 ppm |
| Hot Tubs/Spas | 150–250 ppm |
The Risks of Low Calcium Hardness
When your pool's CH level falls below the recommended range, the water becomes corrosive or "soft". This can have several damaging and irreversible consequences for your pool and equipment.
Problems caused by low CH:
- Surface Etching and Pitting: Soft water will seek calcium from the pool's interior surfaces, leading to the erosion of plaster, tile grout, and concrete.
- Liner Damage: For vinyl and fiberglass pools, corrosive water can reduce the liner's plasticity over time, causing it to fail prematurely.
- Metal Corrosion: Water will aggressively attack metal components like ladders, pump connections, and heat exchangers, leading to rust, staining, and equipment failure.
How to Increase Calcium Hardness
If testing reveals low calcium levels, you can easily raise them by adding a calcium hardness increaser, typically calcium chloride. It is important to follow the product's instructions carefully. A common method is to pre-dissolve the chemical in a bucket of water before slowly adding it to the deep end of the pool with the pump running. This ensures it distributes evenly and avoids localized scaling.
The Issues with High Calcium Hardness
High calcium hardness, or "hard water," occurs when levels exceed the recommended range. This causes the water to become supersaturated, leading to a host of other problems.
Problems caused by high CH:
- Scaling: Excess calcium precipitates out of the water, forming a hard, white or grayish scale on pool surfaces, tile, and equipment.
- Cloudy Water: High mineral content can make your water appear cloudy and hazy, detracting from its clarity.
- Clogged Filtration: Scale can build up within pipes and filters, reducing circulation and the efficiency of your filtration system.
- Heater Inefficiency: Scale can act as an insulator on a pool heater's components, decreasing its heating efficiency and potentially causing it to fail.
How to Lower Calcium Hardness
Reducing calcium hardness is a more difficult process than raising it. The most common and effective method is to partially drain the pool and refill it with fresh water that has a lower calcium content. Alternatively, a sequestering agent can be added to help hold calcium in solution and prevent it from depositing as scale. For pools with cartridge filters, a flocculant can be used to clump calcium particles, which are then vacuumed to waste to avoid clogging the filter.
How to Test Your Pool's Calcium Hardness
Regular testing is essential for maintaining proper water chemistry. You can measure your pool's CH level using a quality liquid drop-count test kit or test strips. While test strips offer quick results, drop-count kits are generally more accurate. It is recommended to test your water regularly, especially if you live in an area with hard source water or use calcium-based chlorine products.
Conclusion
Maintaining a normal calcium hardness level is foundational to proper pool maintenance. By understanding the ideal range for your pool's surface, you can prevent expensive and often irreversible damage from either corrosive soft water or unsightly hard water scale. Regular testing and timely adjustments ensure a balanced, safe, and pleasant swimming environment. For more detailed information on maintaining your pool's water chemistry, consult the resources available from industry experts like Taylor Technologies.
