Maintaining the right Total Hardness in your pool is essential for protecting pool surfaces, equipment and overall water quality. In swimming pools, Total Hardness and calcium hardness are commonly used to describe the same measurement — the amount of dissolved calcium in the water. If hardness levels are too low or too high, they can contribute to surface and equipment damage and ongoing water maintenance issues.
This article explains what Total Hardness means, why it matters and how to keep your pool water properly balanced.
The ideal calcium hardness level for pools is 200–400 ppm (parts per million)
What Is Calcium Hardness in a Pool?
Calcium hardness measures the amount of dissolved calcium (and some magnesium) in your pool water. It plays a key role in overall pool water balance, along with pH and Total Alkalinity. Low calcium hardness = soft, corrosive water. High calcium hardness = hard, scale-forming water.
Low Calcium Hardness in Your Pool
When pool hardness is low (below 200 ppm), the water becomes corrosive and starts pulling calcium from your pool surfaces and equipment. Problems caused by low hardness include:
- Eroding of tile grout and delaminating of plaster surfaces
- Etching or pitting of pool decks or stone and concrete surfaces surrounding your pool
- Corrosion of metal components (ladders, pipes, filters, screws)
- Damage to pool walls and flooring
Important: Damage caused by low calcium hardness cannot be reversed — it must be repaired or replaced.
How to Increase Calcium Hardness in Your Pool
If your pool calcium hardness is low, the most common solution is to add a hardness increaser like calcium chloride. This raises calcium levels quickly and helps protect your pool from corrosion and wear.
High Calcium Hardness in Your Pool
When calcium hardness is too high, the water becomes oversaturated, which can lead to scaling and cloudy conditions. Problems caused by high levels of hardness include:
- Cloudy water
- Scale buildup on pool surfaces and equipment
- Clogged filters and reduced circulation
- Potential damage to heaters and pumps
How to Lower Calcium Hardness in Your Pool
If your pool’s calcium hardness is too high, replacing some of the pool water with fresh water can help bring the level back into the ideal range. Depending on how high the hardness level is, a partial drain and refill may be all that’s needed.
Why Does Calcium Hardness Matter?
Keeping calcium hardness balanced helps:
- Prevent corrosion and surface damage
- Reduce scaling and buildup
- Extend the life of pool equipment
- Maintain clear, comfortable water
How to Test Your Pool’s Calcium Hardness
Regular testing helps you catch imbalances early—before they cause damage.
Test Total Hardness with test strips or a water test kit a couple of times a week.
See, Feel and Smell the Difference
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- Uses up to 50% less chlorine*
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* Compared to the minimum EPA recommended chlorine level of 1.0 ppm for a stabilized swimming pool
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