Calcium Hardness Removers

Pool Calcium Hardness Removers - How Do They Work?

Calcium hardness removers effectively lower the amount of dissolved calcium in your pool’s water.

Although this effect is only temporary, these products still make an effective choice for the prevention of scale and other stains, and many pool owners find using them much easier than partially draining and refilling the pool.

In this article, we will talk about what pool calcium removers are and how they work. We also include information about when and how to use one in your swimming pool.

What Are Calcium Hardness Reducers?

Pool calcium removers are products that lower the readings for calcium hardness in your pool and work to prevent scale from forming.

While these products change the form of the dissolved calcium, they do not actually remove it from the water. The only way to truly remove calcium content from a swimming pool is by performing a partial drain and refill of the pool’s water.

How Do Pool Calcium Removers Work?

Most pool calcium removers work by using a hydroxyethylidene diphosphonic acid complex or HEDP.

This acid complex has a chelating effect on metals and minerals in your pool’s water, which means that it reacts with the calcium in your water, to change it into a form that won’t result in calcium scale and other stains.

The chelating effect of HEDPs on calcium is only temporary. Because no calcium molecules are removed from the water, once these chelating complexes begin to break down, calcium levels will return to pre-treatment levels.

The results of pool calcium hardness reducers last for an average of 5 weeks depending on pool conditions.

When To Use A Pool Water Hardness Reducer

Ideal levels of calcium hardness in a pool range from 200-400 parts per million (ppm). You should use a calcium hardness remover when your pool water begins to exceed 400 ppm, or if you notice scale forming below these levels.

Please note that calcium hardness is different from the total hardness of your pool water, and requires different testing methods to evaluate.

Testing strips that measure the total hardness of pool water are not capable of measuring calcium hardness alone. For this purpose, you will need a liquid reagent testing kit.

How To Use A Calcium Remover In Your Pool

Test Your Pool’s Calcium Levels

Before using a calcium remover in your pool, test your pool’s calcium hardness levels. Only add a calcium remover if your levels are near or above 400 ppm.

It is possible to add too much calcium remover to your pool, resulting in undesirably low calcium hardness levels.

Below the lower limit of 200 ppm, your pool’s water begins to develop corrosive properties and will seek out minerals from other sources, including the lining and equipment of your pool.

Because the effects of calcium hardness removers last for an average of 5 weeks, being exposed to corrosive water for this period of time could cause severe damage to your pool’s lining and equipment.

Choose A Calcium Removing Product

Most calcium removing products available all contain the same active ingredient: HEDP. They all tend to have it in a concentration of 350 - 370 g/L.

For this reason, we recommend whichever product is the cheapest. You can purchase it easily online, but you can also find calcium hardness removers available at your local pool supply store.

Add The Product To Your Pool

Measure out an ideal dose of calcium hardness remover, being sure not to add too much product. It is always possible to add more of this product later on, whereas if you add too much now, you will need to use a calcium hardness increaser to readjust, which is a waste of money.

Distribute the product in the pool near the location of your pump’s water return outflow, and then leave the pump running for a period of 24 hours or as otherwise suggested on your product’s packaging.

Retesting Your Calcium Levels

After you have observed the recommended circulation period for your pool calcium hardness remover, you should retest your pool’s calcium hardness levels.

If your calcium hardness levels are still too high, you may opt to repeat the treatment process, being careful not to overdose your pool with HEDPs.


Pool calcium hardness removers are chemical treatments that temporarily lower the amount of dissolved calcium in your pool’s water, therefore reducing the chances of calcium scale developing.

While these products are not a permanent solution to high calcium levels, they make a great temporary fix if you do not have time to drain and refill part of your pool’s water.

If you do end up needing a drain and refill, use this calcium calculator to work out the appropriate amount of water to drain and refill.

Do you have any questions about calcium hardness reducers or when you should use them? Get in touch with us in the comments section, we’d love to help!

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.