Calcium Scale

Calcium Build Up / Scale On Pool - Why? How To Remove It?

Calcium scale buildup on your pool results in unsightly white stains that may look chalky, powdery or crusty. This scale can make your pool look unsanitary, dirty and can have other undesirable side effects, so most pool owners choose to remove it.

In this article we will talk about the causes of calcium scale in pools, why calcium buildup in pools is bad, and how to remove calcium from your pool.

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Causes Of Calcium Scale

Calcium scale forms in a pool when there is more dissolved calcium in your pool water than the water can hold.

Although some calcium hardness in your pool water is actually essential for your pool’s chemistry, letting calcium levels rise too high will lead to the development of calcium scale/staining and can have other adverse effects.

Ideal levels of calcium hardness in a pool range from 200-400 ppm (parts per million). Above this range is when calcium scale and other undesirable side effects start to occur. Please note that calcium hardness is different from the total hardness of your swimming pool.

How To Test Calcium Hardness

You can test for calcium hardness in your pool using a liquid reagent testing kit.

Testing strips that offer measurements for water hardness should generally be avoided because they are only capable of diagnosing the overall mineral content of your water, and cannot measure calcium levels specifically.

To use a calcium hardness testing kit, you will collect a vial of pool water and then add drops of testing solution to this sample as indicated in the instructions.

Once your testing solution is properly mixed, you can compare the colour of the solution you produced to the colour chart provided in order to determine your pool’s calcium hardness levels.

Why Calcium Build Up In Pools Is Bad

Calcium scale is unsightly when it forms on the surfaces of your pool, and can resemble a crusty, white stain. This calcium scale is fairly difficult to remove, and it can also form on surfaces in your pool that are not visible, such as inside of your pool’s plumbing and filter system.

Calcium scale that builds up inside of your pool’s plumbing can be difficult to find and to remedy.

This type of scale on the internals of your pool equipment also leads to an increased likelihood of issues with normal pump and filter operation, which could eventually necessitate expensive repairs.

High levels of calcium hardness in your pool can also produce cloudy water conditions and can be associated with high total alkalinity and pH in your pool, which in turn can lead to chlorine ineffectiveness (particularly for indoor pools).

How To Get Rid Of Calcium Scale

Balance pH And Total Alkalinity

The first thing you will want to do before attempting to remove pool scale is balance the pH and total alkalinity of your water.

Although these levels typically rise when high calcium hardness is present, the ideal range for pH in a pool is 7.2-7.6 while total alkalinity content should fall between 80-120 ppm.

To lower pH and total alkalinity back within normal range, you should use hydrochloric acid or sodium bisulphate, a dry acid. Both of these products affect pH as well as total alkalinity.

To read more about lowering the pH of your pool back within the normal range, check out our ultimate guide on how to lower pH in your pool.

Use A Scale Removing Treatment

After adjusting your pH and total alkalinity, you will need to use a scale/stain removing product. There are different options available for this, but we recommend a stain remover that is added to your pool’s water, rather than a spot treatment that requires more scrubbing.

Our favourite stain remover for calcium scale is the Serious Stain Remover. To use this product, simply add 1.25kg per 25,000L of pool water and leave the solution to stand in your pool for 2-3 days.

Although this approach takes your pool out of commission for a few days, many pool owners find this preferable to scrubbing the scale spots themselves.

The effects of many stain removers can also be further strengthened by creating an abnormally low pH in the pool water before use. Check your product’s information label to make sure this is applicable to your scale remover.

How To Remove Calcium From Pool Water

After you remove calcium scaling, you will also want to remove any high amounts of dissolved calcium in your water so that calcium scale does not return.

Since many stain removal products contain agents that work to sequester calcium in your water and prevent it from depositing on surfaces, it may not be necessary to perform this step if you have recently used a scale removing treatment.

Test the calcium hardness of your pool water to see if this treatment is needed. Calcium hardness levels that are approaching or exceeding 400 ppm should be lowered.

The only real way to remove calcium particles from your pool is by draining and refilling the water with fresh water, but chemicals are also available that can provide a temporary solution if this process is not accessible to you.


Calcium scale occurs in pools when there are high amounts of calcium present in the water. This usually comes from your pool’s source water, but can also be introduced through other chemicals, such as cal-hypo shock treatments.

Luckily, calcium scale can be removed with the right approach to treatment. Stain removers make a great option for low-maintenance scale removal, while draining and refilling to remove calcium from your water will prevent it from recurring.

Do you have any questions about how calcium scale forms in a pool or how you can remove it? Get in touch with us in the comments section, we’d love to help out!

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.