Pool Care Pool Water Chemistry

How to Adjust the Calcium Hardness in Your Pool?

A swimming pool is a luxury that most people wish they had. It’s not just for fun or recreation, though it can be both of these things, but also something that removes the need to pay extra for water that you will swim in.

However, one of the unsuspected causes of problems, calcium hardness, prevents you from enjoying swimming. Today, I will discuss what calcium hardness is, what happens when it’s too high or too low, and how to rectify it.

What Is Calcium Hardness?

Simply put, calcium hardness is the concentration of calcium ions present in the solution, which translates to total calcium concentration. This total can be measured through testing for either free or combined calcium ions.

Pool owners interested in using salt chlorine generators are typically most concerned with total calcium concentrations because they affect how efficiently their chlorinators work.

Keeping this value high ensures that there are enough free calcium ions in the water for these effects. While you can influence calcium hardness through regular maintenance procedures, it’s often helpful to know the exact level of the total chemical content to make any necessary corrections.

It causes a series of issues, including:

  1. The water is so hard it hurts your skin and eyes
  2. Pool staining from calcium deposits
  3. Damages to your pool surfaces
  4. Water becoming cloudy
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What Is the Correct Calcium Hardness Level?

Pool calcium hardness is a measurement of the minerals in a pool’s water. Because these minerals can be harmful to a pool if they clump together in the water, pool owners need to determine what calcium hardness level is safe and effective for their pools.

The correct level of calcium hardness in a pool depends on the pool’s material. For example, vinyl or fiberglass pools should have calcium hardness levels between 175 parts per million (ppm) and 225 ppm. Meanwhile, concrete or plaster pools should have calcium hardness levels between 200 ppm and 275 ppm.

The mineral content in different pools also affects how often it is necessary to remove water from a pool. Vinyl or fiberglass pools are porous, which means that their material absorbs minerals in the water.

That can lead to frequent pool maintenance because the material needs to be cleaned more frequently than most other types of materials would need. By contrast, concrete or plaster pools don’t absorb any minerals in the water, so they only need to be drained once every few years – if at all.

What happens if calcium hardness levels are too high?

When the mineral levels of tap or well water are too high, we say the water is hard. The same happens to pool water. If you do not keep the calcium hardness levels of your pool at a certain level, then you might notice some problems with the water in your pool.

Pool Water Cloudiness: If the calcium hardness levels were too high, you might notice your pool water becoming cloudy. The reason for this is that there is a scale called TDS or total dissolved solids that have positive minerals in them that are beneficial and negative ones that are not good for the water.

Calcium sediment: Calcium hardness is made up of calcium and bicarbonate ions. These two substances get mixed up with the salt in your pool and get deposited down on certain surfaces, which can be very difficult to get rid of. If the levels were too high of the mineral calcium, you might notice a white film starting to cover walls and even equipment like heaters that might start bubbling because of the scale build-up on them.

How Do You Lower Calcium Hardness?

Lower calcium hardness levels can be challenging since no go-to chemical can help raise the water hardness. But, after research, the following tricks can help:

Drain Some Water and Refill: You may need to raise calcium hardness if you notice cloudy, hazy pool water or a low concentration of total dissolved solids. To increase calcium hardness levels, drain a portion of the water from your pool and refill it with fresh filtered tap water with a lower calcium level.

Use a Sequestering Agent: Then, either dilute or remove excess minerals by adding a sequestering agent, which binds with metals in the water to allow easier removal by filtration. When using pool sequestrant, follow the directions on the package label and let stand for 12-24 hours before draining some water.

Use Muriatic Acid: Next, add muriatic acid to the pool at the rate recommended in the label instructions or by your local pool store’s technician. Maintain this level of calcium hardness for several months to ensure it is stable in the water. A good rule of thumb is to add muriatic acid at a rate equivalent to one gallon per 500 square feet, but not more than 5 gallons per 1000 square feet over two days. Typically you should wait 24 hours before adding any more acid once you have added your initial dosage.

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What happens if calcium hardness levels are too low?

It’s not unusual for water to start with high calcium hardness, but the level gradually declines as water is used up through daily activities. But what happens if calcium levels are too low?

Pool surfaces start to erode since the pool does not have adequate Calcium ions present in the solution to protect them chemically. At this point, the water will need some water balance correction and mineral replenishment.

The pH level also declines at lower calcium hardness levels because the limited calcium concentration is inadequate to buffer rising acidity. As a result, total alkalinity (TA), acid demand (pH), and calcium hardness levels decline.

When this happens, corrosion will occur, and metal parts will erode, causing rust and calcium stains will form on pool surfaces and scale development that starts on tile grout lines. Plaster surfaces appear duller than usual, staining increases on fiberglass wall panels, and vinyl liners look gray instead of their standard color.

Effects may not be seen for several weeks or months after calcium levels drop below optimal concentrations.

How Do You Raise Calcium Hardness?

Raising calcium hardness is much easier than lowering it. All you need is an ideal calcium hardness increase, such as calcium chloride. It is the go-to product that can help you raise your pool’s calcium hardness and give control over how much calcium is in your swimming pool.

You can also add calcium as a by-product of using unstabilized chlorine (calcium hypochlorite), famously known as Cal-hypo. It’s a sanitizer used pool shock treatment.

The downside of adding Cal-hypo frequently is that it can end up adding too much calcium to your pool water, creating another problem. What’s more, if you use it as pool shock treatment, the chlorine will be used up and leave more calcium in the water.

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So, how to add calcium chloride to raise pool calcium hardness

Things you will need:

  • Test Strips or Testing Kit (Capable of Testing Calcium Hardness)
  • 5-Gallon Plastic Bucket
  • A Wooden Stir Stick
  • Safety Gear (Gloves and Goggles)
  • A Dry Measuring Cup
  • Calcium Chloride (Flake or Granular)
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Step 1. Test and Balance Your Pool Water

Test the pool water to make sure the pool chemistry is balanced correctly. If not, add the necessary chemicals to balance it.

You want to make sure the levels are as shown below:

Pool ChemicalPool Chemical Levels
Chlorine1 – 3 ppm
pH7.4 – 7.6
Total Alkalinity80 – 120 ppm (parts per million)

While buying the testing kit, you want to buy a product that can test all the above chemical levels and calcium hardness. So, it’ll be best to double-check to be sure. Most digital pool chemistry testing kits should have an issue.

Step 2: Test the Calcium Hardness Levels

Once you’re sure the pool chemistry is balanced, test the calcium hardness levels to determine the amount available and how much you need to raise it to the proper levels.

Step 3. Calculate How Much Calcium Chloride You Need

Before adding the calcium hardness increaser, you want to know how much you need to raise the water hardness, and the decision is based on your pool size and volume (amount of water it holds.)

A general rule of thumb; if you want to raise your pool calcium hardness by 10 ppm, you will need to add two calcium chloride ounces to 1000 gallons of water.

So, suppose your swimming pool’s capacity is 10,000 gallons of water, and the calcium hardness level is 20 ppm less; you’ll need 40 calcium chloride.

If you don’t know how much water your pool hold, you can use the online calculator below:

Step 4. Gear Up

Now that you know the amount of calcium chloride to add to your pool water, it’s time to get ready to get your hands dirty. Wear protective gear, both gloves, and goggles.

Dry calcium chloride isn’t dangerous. But when you add it to water, it tends to get hot, and if you’re not extra careful, it can burn you. That’s why I strongly advise you to wear chemical-resistant gear – gloves and goggles.

Step 5. Mix the Calcium Chloride with Water

Take the 5-gallon plastic bucket and dip it into your swimming pool; fill it 3/7-full. Get the dry measuring cup and fill it with calcium chloride and pour the contents into the bucket.

Pro tip: for safety reasons, it’s always good to add the chemicals to the water and not water to the chemicals.

Use the wooden stick to stir the solution until all the calcium chloride is dissolved fully. If it’s taking too long, you can get a chelating agent such as SC-1000 to speed up the process.

Step 6. Pour the Solution into the Pool Water

Take the solution and carefully pour it into the swimming pool as you water around the pool perimeter.

You want to make sure the pool pump is running to help circulate the calcium solution to all the pool corners. I also recommend you brush the walls to help distribute the calcium chloride.

Wait for the pool pump to meet the pool turn-over rate before retesting the calcium hardness levels.

Step 7: Retest and If Needed, Adjust the Pool Chemical Levels

Once the circulation is done and you’ve confirmed that the calcium levels are between 175 – 225 ppm for vinyl or fiberglass pools and 200 – 275 ppm for concrete or plaster pools, retest the general pool chemistry to get them back to the levels in the table above. You can adjust them if necessary.

How to Avoid Calcium Hardness Increase or Decrease

Did you know you can avoid the calcium hardness fluctuation in your pool? It’s pretty straightforward. All you need to do is:

  • Keep your swimming pool clean by maintaining it regularly.
  • Test and balance the pool water chemistry frequently – test it weekly or bi-weekly using a test kit capable of testing calcium hardness.
  • You want to make sure you keep a close eye on Total Alkalinity and calcium hardness. Address the problem as easily as possible. Avoid waiting till things get out of hard.

Related Questions

Can you swim in a pool with high calcium?

No! Even though the effects of high calcium hardness are felt more by the swimming pool, they can also affect the swimmers. With the calcium levels too high, you might get irritation to the eyes and skin.

About the author

Sharif Miah

Hi! I'm Sharif, the founder of Globo Pool® and I have been working in the pool & hot tub industry for the last few years. I love to share my experiences with people & hope you are enjoying my information and lessons!

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