How to Balance and Maintain the Calcium Hardness Level in Your Pool

Written by Michael Dean
September 14, 2023

balancing calcium hardness in swimming pool

Getting your pool chemicals just right is a science. It’s your best defense against cloudy or dirty water, but it takes practice to perfect. While the most stressed chemical levels to balance are pH, chlorine, and alkalinity, you should not neglect your calcium hardness. Calcium hardness plays a pivotal role in your pool ecosystem, and learning how to maintain and balance it is imperative.

Below, you’ll learn about what calcium hardness is, why maintaining it is vital to the quality of your swimming pool, and how to optimize your levels. For more on water chemistry, make sure to read my complete guide on essential pool chemicals.

Main Takeaways

  • Your plaster or concrete pool should have a calcium hardness of 200-275 ppm, and your fiberglass or vinyl pool should be at 175-225ppm.
  • Test your calcium levels every 2-3 weeks, but also when you drain your pool or add new water or chemicals.
  • To lower calcium hardness levels, drain and replace the water, use flocculant, or use muriatic acid.
  • To raise calcium hardness levels, use a calcium hardness increaser.

What Is Calcium Hardness?

Calcium hardness is a measurement of how much calcium is in your pool water. Most water used to fill pools has some amount of calcium present. So, you’ll need to test this mineral level to make sure it is optimal for your pool.

The calcium content of your pool water works in harmony with the pH, alkalinity, and chlorine.

What Is the Role of Calcium Hardness?

Calcium works with other pool chemicals to keep your pool water healthy and clean. When the calcium hardness is below 175 parts per million (ppm), it is considered “soft.” Soft water can cause your pH levels to drop and your pool water to become acidic and corrosive.

On the other hand, if there is too much calcium in your water (more than 275 ppm), your pool water is considered “hard.” Hard pool water causes a build-up of calcium on your pool surfaces and equipment, as well as cloudy water

Neglecting your calcium hardness level can lead to issues such as scaling, corrosion, etching, cloudy water, and, in severe cases, you may even have to replace your plumbing and equipment!

You can prevent these issues by simply testing your calcium levels frequently and adjusting them as necessary.

Why Is Maintaining Calcium Hardness Important?

As I mentioned, unbalanced calcium hardness can wreak havoc on your pool in a number of ways. In extreme cases, excess calcium can build up in your plumbing, clog your pipes, and stop or slow your water circulation. Low calcium hardness can make the water acidic, damaging and corrode your pool plaster. Not to mention that acidic water is dangerous for swimmers!

Getting to the Right Calcium Hardness Levels

Here’s a guide on the ideal calcium hardness levels and how to get them just right. You can use my calcium hardness calculator to figure out how much calcium hardness increaser to add or pool water to replace.

What’s the Right Level of Calcium Hardness for Your Pool?

A few factors will determine the optimal calcium hardness level, such as the type of pool you have. If your pool is plaster or concrete, you need to aim to keep your calcium hardness at around 200-275 ppm (parts per million). If it’s fiberglass or vinyl, I recommend keeping it at 175-225 ppm.

How to Test Your Calcium Hardness Levels

You should test your calcium hardness levels every 2-3 weeks. The most efficient testing method is a liquid drop test because it will give you the most accurate reading. You can also use testing strips, but they will provide a more approximate reading. For more information on using a testing kit, check out my guide for testing pool water.

Effects of High Calcium Hardness on a Pool

High calcium content in your pool water can cause the following:

  • Damage to your pool walls and equipment
  • Scales of minerals built around the pool walls and equipment
  • Rough pool surface
  • High pH level
  • Cloudy water
  • Clogged filters

How to Lower High Calcium Hardness Levels

If you test your water and find that the calcium hardness is too high, a few simple processes will help you get your pool back in shape.

Replace Some of the Water

The first option is to drain some pool water and replace it with fresh water. Make sure to test the water before and after refilling the pool to ensure you have calculated correctly. However, if the tap water in your region is high in calcium, this may not be a viable option.

Use Pool Flocculant

Flocculant is a chemical that will cause the excess calcium to clump together. When these clumps form, they sink to the bottom of the pool, and you can then use your vacuum to remove them.

Remember to turn off the filter and the pump before adding the flocculant. If flocculant gets into your filter medium, you must replace it. Don’t use flocculant if your pool uses a cartridge filter.

Use Muriatic Acid

Try adding some muriatic acid as a last resort. Though this chemical doesn’t lower the calcium hardness in your pool, it does increase the level of saturation, which can balance out your pool water.

Effects of Low Calcium Hardness on a Pool

If your water has low calcium hardness, it is classified as ‘soft’ water. Soft water can lead to the following issues, all of which can result in expensive pool repairs:

  • Corrosion of metal equipment
  • Dissolving of plaster, concrete, stone tiles, and grout
  • Etching of pool surfaces, including pool decking

How to Raise Low Calcium Hardness Levels

The good news is that increasing the calcium hardness in your pool is a lot easier than decreasing it. You can purchase a calcium hardness increaser (like calcium chloride) that will raise your levels when added to your water. Calculating the volume of your pool will help you work out how much of the product to purchase.

You’ll often see this product labeled as “calcium hardness increaser” or “hardness plus,” like Leslie’s pool supply store does in the photo I took below.

Here’s the same Hardness Plus product on Amazon if you don’t have a Leslie’s pool supply store near you.

Leslie's Hardness Plus for Calcium Hardness, 4 lbs.
View on Amazon
I may earn a commission if you make a purchase, at zero additional cost to you. This in no way impacts my research process or opinions.

Tips for Maintaining Your Calcium Hardness Levels in the Right Range

Although calcium hardness can be an easy fix, it’s a pain when your pool water levels aren’t balanced properly. Ideally, your calcium hardness levels should be in the correct range at all times.

Here are my best tips for doing this:

1. Keep Your Water Levels Balanced

The easiest way to maintain your calcium hardness levels is to check your pool chemistry frequently. Also, keep an eye out for any changes, especially regarding calcium hardness.

2. Face Any Potential Problems Head-On

You should address any issues as soon as you notice them. For example, don’t wait until your water is too hard. If you see the level increasing, take action immediately.

3. Test Your Water Regularly

Ideally, you should test your pool water every week, especially if your water source is hard. You should also check the calcium hardness every time you drain the pool and add new water or chemicals. If you’ve had torrential rain recently, it’s also a good idea to test. The best test kits are usually liquid kits, but test strips work, too. Just make sure your test kit includes a test for calcium hardness.

4. Keep Your Pool Clean

Last but certainly not least, keep your pool clean. Keeping your pool clean is a surefire way of staying on top of your pool water’s chemistry levels. Clean it out if it’s stormed lately in your area and you notice debris in your swimming pool.

As long as you’re observant about your chemical levels (particularly calcium hardness, total alkalinity levels, pH, and chlorine levels), you should have no problem.

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

How do you fix calcium hardness in a pool?

Calcium hardness should be between 200-275 ppm for a plaster or concrete pool or 175-225 ppm if you have a fiberglass or vinyl pool. If your calcium hardness levels are too high, drain the pool and replace the water, use a flocculant, or use muriatic acid. Conversely, if your levels are too low, use a calcium hardness increaser.

What causes excess calcium in a pool?

Your calcium hardness levels may be out of wack for many reasons, including hard tap water, high pH, evaporation, lack of water circulation, and fluctuating temperatures.

How do you remove calcium buildup and scaling in a swimming pool?

To remove calcium scale deposits, first, lower the calcium hardness level, get the alkalinity back to 80-120 ppm, check the pH level, and finally, use a scale eraser and scale remover to scrub away the scale.

Feel free to reach out to me with any questions!

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