How to Lower Calcium Hardness In Your Pool

Written by Michael Dean
March 16, 2023

lowering calcium hardness in a swimming pool

Summer is here, and it’s time to enjoy a refreshing dip in your pool. But if you’ve noticed cloudy water, scaling on the pool surface, or decreased effectiveness of pool chemicals, it may be time to check your calcium hardness levels. 

In this article, I will go over a few steps to help you lower calcium hardness in your pool, explain what cases high levels, and give a few useful pointers on how to keep it in check, so let’s get into it!

Main Takeaways

  • Hard water can be caused by high calcium deposits in your groundwater supply, evaporation, and calcium-based chemicals.
  • Water that is too hard can damage your pool equipment via calcium buildup; water that is too soft can make water corrosive and stain pool surfaces.
  • Some ways to keep calcium levels balanced include: testing the water regularly, monitoring water sources, and checking your pool chemicals.

Step-by-Step Guide: How to Lower Calcium Hardness In Your Pool

Here’s my step-by-step guide to help you lower the calcium hardness levels in your pool. You can also use my calcium hardness calculator to help.

Step One: Test

Test your pool’s calcium hardness level and determine your current calcium levels. Calcium hardness should ideally be:

Step Two: Partial Drain-and-Refill (Option 1)

The most effective way to reduce calcium hardness is by partially draining your pool and refilling it with fresh water. If your local water supply source is not high in calcium, this is the best way to reduce calcium levels.

To do this, drain some of the water (how much you’ll have to drain depends on how high the calcium levels are) and then refill it with fresh water.

Step Two: Use a Flocculant (Option 2)

The first method won’t work if your local water supply is high in calcium. In this case, you’ll need to use a flocculant instead.

A flocculant can help gather the calcium particles and settle them to the bottom of the pool in clumps so that you can vacuum them out. Keep your pump and filter turned off during this process.

Step Three: Monitor Calcium Levels

Once you have lowered your pool’s calcium hardness level, it is essential to maintain it within the recommended range. Test your pool’s calcium levels monthly and adjust accordingly to prevent any issues from recurring.

How to Test For Calcium Hardness Levels

You can test for calcium hardness levels using either test strips or a liquid drop test kit.

Using a test strip is relatively straightforward. You just need to dip the test strip in the pool elbow-deep, then compare the color on the strip with the manufacturer’s chart.

A liquid drop test kit is slightly more complicated and involves adding drops from 3-4 different regents into a water sample until it reaches the right shade of blue. Other liquid drop test kits simply require a few drops of reagent into the water sample and comparing the color with the manufacturer’s color chart.

What Causes High Calcium Hardness Levels?

High calcium hardness levels in swimming pools can be caused by a variety of factors. 

Hard Water

If you use hard water to fill your pool, the calcium levels in your pool water may be high. If you’re unsure about your local water supply’s chemical makeup, call your municipal water authority and ask.

Use of Calcium-Based Chemicals

A common culprit of high calcium hardness levels in pools is calcium hypochlorite, a popular pool chlorine sanitizer. Using it to shock your pool can lead to high calcium hardness levels.


This might sound obvious, but evaporation can be a source of high calcium hardness levels. When water evaporates from your pool, the calcium and other minerals in the water become more concentrated, leading to high calcium hardness levels.

Unbalanced Water Chemistry

Pool chemicals are easily affected by many elements, including each other. If your pH and total alkalinity levels are out of wack, this can lead to calcium deposits on your pool surfaces, among other issues.

What Happens if the Water is Too Hard?

If the water in your pool is too hard, it can lead to several problems:


High calcium levels in the water can cause scaling on pool surfaces, which can be challenging to remove, make the pool look unsightly, and can hurt swimmers due to the rough surface. Such buildup also means calcified deposits on your pool fixtures, plumbing equipment, pipes, and valves, damaging your pool overall.

Cloudy Water

Excess calcium in the water can cause the water to become cloudy, making it difficult to see the bottom of the pool, which can be dangerous. Plus, it is not nice to look at!

Increased Maintenance Costs

Fixing the aftermath of high calcium levels on your equipment can be pretty expensive, with plumbing, pipes, heaters, and filters potentially needing parts repaired or replaced entirely. Furthermore, removing calcium scale deposits may require several hours of hard labor—scrubbing away at spots of calcium residue with a pumice stone.

What Happens if the Water is Too Soft?

Just as hard water is bad for your pool, so is pool water that is much too soft. Here’s why:


Soft water can be corrosive, causing damage to pool surfaces and equipment, including metal pipes, heaters, and pumps. The corrosion can also cause stains on pool surfaces and equipment, such as plaster, tiling, or liner.

Algae Growth

Soft water is preferred by algae, making it easier for algae to grow in the pool.

Increased pH levels

Soft water will also increase the pH levels, making it more difficult to maintain the proper chemical balance and reducing the effectiveness of the chlorine in your pool.

Tips for Keeping Calcium Hardness Levels Balanced

The best thing to do for your pool is to avoid your calcium hardness levels going out of wack in the first place. Here are my top tips to help you keep your levels balanced. If you ever find your calcium hardness level too low, bookmark my article on raising calcium hardness.

Test Your Pool Water Regularly

You need to test your pool water for calcium hardness levels regularly – at least once a month. Calcium levels tend to be stable, but rain, algae, and other pool chemicals can easily affect pH, alkalinity, and calcium levels. So, regularly testing your water is the best way to spot any imbalances early and correct them before it’s too late.

Check Your Pool Chemicals

Keep an eye on the chemicals you use in your pool, especially if they’re calcium-based. The most common pool chemical used that contains calcium is calcium hypochlorite, a type of pool shock. Using too much can cause calcium buildup in the water, so monitor your usage carefully.

Monitor Water Sources

If you use hard water to fill your pool, consider using a water softener to remove excess minerals before adding the water to the swimming pool. And if you live in an area with heavy rainfall, get a pool cover to shield your pool from contaminants.

Get My Free Pool Care Checklist

Download my free, printable pool maintenance checklist to help you accomplish regular pool care tasks for any type of swimming pool.

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Frequently Asked Questions

Can you swim in a pool with high calcium hardness?

Technically, yes, you can still swim in a pool with high calcium hardness levels. While not harmful, I wouldn’t recommend it. High calcium levels can make your skin, eyes, and hair feel rough, brittle, dry, and coarse.

What’s the most effective way to decrease calcium hardness?

The most effective way to decrease calcium hardness in your pool is to partially drain and refill the pool with fresh, clean water. But if the freshwater is high in calcium, the next best method is to use a flocculant.

Will baking soda lower hardness in a pool?

Baking soda can increase the pH and total alkalinity in your pool, which indirectly helps stabilize calcium hardness levels, but it is not an effective method for lowering calcium hardness levels. In fact, be careful when adding baking soda to hard water, as having a too-high pH can cause calcium buildup in your pool.

Will muriatic acid lower hardness in a pool?

Muriatic acid is typically used to lower pH and total alkalinity levels in a pool, but it does not significantly impact calcium hardness levels. With that said, although muriatic acid doesn’t directly lower calcium hardness levels, it will increase the level of saturation, balancing out your water, albeit in an indirect way.

Do you have any more questions about high calcium hardness levels or any other topic? Shoot me a message; happy to help.

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