What is Calcium Hardness?

Like any swimming pool chemical, calcium hardness must be balanced and managed in order to maintain a healthy swimming environment. The present industry standard for calcium hardness is from 200–400 ppm in swimming pools and 150–250 ppm in hot tubs.

Total Hardness

The “total hardness” of your swimming pool water is based upon elements of calcium and magnesium salts. However, the calcium component is the focus for balancing pools, hot tubs, and spas. The Saturation Index (SI) is a formula that measures the hardness of your swimming pool and considers the relationships between five factors:

  • Calcium Hardness
  • pH
  • Total Alkalinity
  • Cyanuric Acid (used as a stabilizer in the SI formula)
  • Temperature (Fahrenheit)

When the SI reads zero, your pool water is perfectly balanced. If the SI value reads +0.5 or higher, it is unbalanced. This creates an environment in which calcium carbonate scales the surface and lining of your swimming pool. If your SI value reads at -.03 or less, your pool is leaning towards corrosive behavior. A corrosive swimming environment will eat away at grout, concrete, and metal, leaving surface stains and contributing to water discoloration.

Read more about the Calcium Saturation Index here.

Effects of High Calcium Hardness

  • Clogged filters/reducing circulation
  • Inefficiency of pool heater
  • Cloudy water
  • Rough surfaces caused by scale build-up

Effects of Low Calcium Hardness

  • Dissolves gout
  • Concrete pitting on surface/deck
  • Plaster etches

Saturation Index (SI) Troubleshooting

So, how do you reverse the damage done by scaling and corrosiveness? Unfortunately, if your swimming pool has taken a dive into corrosive values, there is no quick way out. The maintenance in order to repair a corroded pool is to replace the concrete and piping. There are “metal out” cleaning mixtures that can be used to cure the discoloration in your pool water, some of which have been known to remove surface stains as well.

In order to repair scaling pool water, you must reduce the SI level to about -1.0, which is often done by lowering a pool’s pH level. Once at this reduced value, calcium deposits in the filter and piping can be dissolved, and the water’s flow may even remove chunks of loosened scale. As any seasoned pool owner knows, balancing your pool water is tricky and not for the faint of heart. As a result of lowering the pH, a layer of concrete surface may dissolve, contributing to copper loss from piping and/or heat exchangers.

Test the values of your pool chemistry often using test strips/kits to ensure the safety and stability of your pool.
Try out our Pool Calculator as you test the values in your pool! For more information on how to care for your pool, see our blogs on Pool Maintenance

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