Reduce Calcium Hardness

How To Reduce Calcium Hardness In A Pool?

Keeping your pool’s chemistry balanced can be a challenge. Many different pool chemicals and other dissolved components in your water can interact with each other, causing a variety of unwanted side effects.

Calcium hardness is one of the properties of your water that is known to fluctuate from pool to pool, and react with other chemicals in the pool.

While low calcium hardness can cause pitting and corrosion of your pool liner, high levels of calcium hardness can be equally bad. It can lead to the development of unsightly scale as well as other related complications.

Read on to learn more about the ideal levels of calcium hardness for pools, how to identify high hardness levels, the problems associated with high calcium hardness, and different ways that you can work to reduce your pool’s calcium hardness content.

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Ideal Calcium Hardness for Pools

Before taking steps to balance your pool’s chemistry, you need to know the normal levels of calcium hardness that your pool should maintain. The ideal range for calcium hardness in your swimming pool is 200-400 parts per million (ppm).

High levels of calcium hardness above this range can lead to a variety of problems in your pool, which we will discuss shortly.

How to Identify High Hardness

In order to identify high levels of calcium hardness in your pool water, you will need to use a test kit capable of identifying the concentrations of this dissolved mineral.

Problems Associated with High Calcium Hardness

There are many problems associated with high calcium hardness in your pool water, but the most prominent and well-known of these problems is the development of scale, also known as calcium deposit stains.

Calcium Scale & Deposits

Calcium scale shows up as a layer of white, chalky colored substance (typically made of calcium carbonate - CaCO₃) that attaches itself firmly to your pool’s surfaces.

Scale is highly resistant to attempts at scrubbing. Although not impossible to remove, it can be very time consuming. It can be particularly tricky to clean from some pool surfaces, like pebblecrete, so prevention is the best option.

Scale can also be a sign that there are other problems with your water chemistry. While the concentration of calcium is important, high pH and total alkalinity increases the concentration of carbonate in the water, which is the other half of the scale compound.

High calcium + high carbonate leads to scale formation.

Cloudy Water

High calcium hardness in your pool can also lead to cloudy water. Cloudy water is a sign that your pool has high enough calcium levels that scale is starting to spontaneously form in your water.

Occasionally, high calcium hardness induced cloudiness also causes clogs in your filter system, which can lead to poor circulation. You are likely to notice a rapid increase in cloudy water once your filter has been clogged by high amounts of solid calcium.

Bacteria & Algae Growth

Poor circulation caused by a clogged filter (that is overloaded with calcium deposits) also has numerous other potential side effects, such as a buildup of organic debris in the pool and the development of algae or other bacteria due to chlorine being consumed more rapidly and being poorly circulated.

You will find yourself adding more chlorine and backwashing more frequently unless you get on top of this calcium problem quickly.

How to Reduce Hardness

There are two main methods for removing high concentrations of calcium hardness from your pool water. These include using a product known as a calcium remover, or performing a partial drain and refill of your pool water.

If your calcium hardness levels are exceptionally high, a combination of both of these approaches will work best.

Drain & Refill

To begin, we recommend performing a partial drain and refill of your pool’s water.

As your pool water evaporates through normal use, residual calcium particles are left behind, slowly growing in quantity in your pool until a problem develops.

The only way to genuinely remove these calcium particles from your water is to drain some of the water, and fill it from a source with a lower calcium hardness content than what is present in your pool.

This cannot be achieved by topping off your pool with fresh water unless a large amount of water is drained beforehand.

Topping your pool off with fresh water will dilute the amount of calcium in your pool, which can provide lower calcium hardness readings temporarily. However, adding more water does not actually remove any calcium unless you drain some of the old water first.

Use this calcium hardness calculator to work out how much water to drain and refill for your pool.

Once you have drained and replaced part of your water, you should balance your pool’s pH, total alkalinity and chlorine. Once you have corrected these levels, re-test your calcium hardness.

Certain pool treatment chemicals that affect your pH and total alkalinity can have a lowering effect on the dissolved minerals in your pool.

Calcium Hardness Remover

If you still have high calcium hardness readings after following these steps, we recommend that you use a calcium hardness remover.

Although the chemicals in calcium removing products do not actually remove these calcium particles from your pool, they do cause them to change in form and become chemically inactive.

This prevents the dissolved calcium from accumulating on your pool’s surfaces and causing scale or other damage.

Because calcium removing products work to prevent scale and related issues with high calcium, they can be very helpful to use.

However, if you have a high calcium problem with your pool, draining it partially and refilling it is the only adequate way to genuinely remove some of the dissolved calcium content from your pool’s water.


Although pool calcium hardness can be somewhat difficult to manage due to its effects on other water properties, adjusting your levels to get them back down within normal range can be a fairly easy process.

Because high levels of calcium accumulate in your pool through normal water evaporation, performing a water change is a necessary part of treatment in order to remove residual minerals.

Do you have any questions about how to reduce calcium hardness in a pool? Leave us a comment down below, we’d love to hear from you!

Louis from Pool Advisor


A chemical engineer by trade, Louis is committed to debunking myths in the pool industry by explaining the underlying chemistry and making it accessible to all.