How To Remove & Prevent Calcium Scaling

Pool Care Chapters

There are several factors that we need to use to fight calcium scaling. We recommend that you take the time to understand them. If you don’t have time for that right now, you can just use our guide to help you remove the scaling.

How to Remove Calcium Scaling at the Waterline

Calcium scaling within the water can be fixed when we balance out the pool chemicals. Calcium scaling at and above the waterline will require a more hands-on approach:

  • Step 1: Drain a little bit of water to expose the calcium scaling fully
  • Step 2: Use a large wire brush to scrub off large pieces of calcium scaling.
  • Step 3: While wearing acid-resistant gloves, fill an acid-resistant spray bottle with muriatic acid. You can use alternative acids, but they will need to have a comparable pH scale.
  • Step 4: Scrub some more
  • Step 5: Repeat earlier steps as needed.

How to Adjust Water Chemicals to Remove and Prevent Calcium Scaling 

Once you have removed the calcium scales, you can prevent calcium scaling from forming by performing the following series of steps:

  • Step 1: Use a thermometer and a chemical testing kit to measure the following
    • Alkalinity (Carbonate aka dissolved baking soda)
    • Water Hardness (Calcium)
    • Water Temperature
    • pH (Hydrogen)
    • Total Dissolved Solids (TDS)
  • Step 2: Use those measurements to find their matching factors in the chart at the top of this page.
  • Step 3: Input those factors into the following equation to find your place on the Langelier Saturation Index.
    • LSI = pH factor + Temperature factor + Water hardness factor +
      [Alkalinity ppm (CYA ppm x Cyanuric correction factor)] – TDS factor
  • Step 4: When you know your current LSI number, make adjustments to your pool chemicals to bring that number as close to zero as possible. If you want to remove calcium scaling, bring that number slightly into the etching side of the LSI scale. As the acid removes the calcium from the walls, it brings the LSI number back to 0.

What to Adjust to Correct LSI Numbers

Balanced: 0.3 to -0.3

The chemicals are balanced. You do not need to remove water or add chemicals.

Corrosive: -0.3 or less

If the pool is corrosive, increasing any of the following will help to increase the LSI and reduce the etching.

  • Increase temperature
  • Increase alkalinity
  • Increase pH (reduces acidity)
  • Increase calcium

Scale Forming: 0.3 or more

If the pool is on the scaling side of the LSI, you can reduce it by

  • Increasing stabilizer
  • Decreasing temperature
  • Decreasing pH (Increasing acidity)
  • Draining water to Reduce the total dissolved solids (You’ll need to rebalance the chemicals if you do this one)

Okay, those are the basics of how to fix an immediate calcium scaling problem. Now, we are going to shift our focus to more generalized guidelines. We’ll show how you can fight high calcium levels that lead to calcium scaling and a bit of the science behind it. Here are some of the upcoming sections. You can click on the links to skip to that section of the guide:

  • Preventing Calcium Buildup
    • Sequestering Agents
  • Slowing Calcium Growth
    • Reverse Osmosis Filtration
    • Switch from Calcium Hypochlorite
  • Reducing High Levels of Calcium
    • Raising pH and Adding Flocculants
  • Environmental Factors
  • Questions and Answers

What Can You Do to Fight Calcium Scaling

Preventing Calcium Buildup

Tap water contains plenty of calcium. If you don’t plan on using a reverse osmosis filtration system, you will likely be adding calcium every time you fill up your pool. Since calcium won’t evaporate but water will, your pool’s calcium levels will continually rise until you have no choice but to remove it.

We can counter calcium buildup with water acidic enough to dissolve any calcium attempting to latch onto the pool’s surfaces. That means we need to maintain a pH of 7.2 to 7.4 and an alkalinity of 80 to 100. If your pH is too high (acidity too low), you can lower it with muriatic acid. 

Binding the Calcium with a Sequestering Agent

Sequestering agents are a great way to control the adverse effects of calcium buildup, but they are certainly not perfect solutions. While they might not be perfect, they will allow you to put off the task of reducing the calcium for a while.

Sequestering agents bind to metallic ions. If you use one that’s developed to bind to calcium, you can keep the calcium from building up on the surfaces of your pool.

How to Slow Calcium Level Growth

Over time, as we add products and contaminants infiltrate the pool, the total dissolved solids will increase. When the pool becomes oversaturated with these dissolved solids, the chlorine becomes increasingly ineffective. 

If you’ve noticed that your chlorine isn’t as effective as it used to be, and the sequestering agent just isn’t fixing the problem, it’s likely that there are too many dissolved solids (TDS) in your pool, and a lot of these dissolved solids are probably calcium. At this point, you need to drain some of the pool or use an alternative method to extract the calcium.

Draining a portion of your pool’s water is the simplest solution to reducing an overabundance of calcium. However, depending upon where you live and any potential drought conditions, this might not be a viable option for you. In that case, here are a few alternative methods to reduce your pool’s calcium content.

Reverse Osmosis Filtration

Many of you are likely familiar with reverse osmosis filtration systems. They are the vanguard filtration systems capable of removing the most stubborn impurities from water. Some homeowners install them within their homes to remove fluoride, and some install them to remove calcium from the water used to fill up their pools.

These are not replacements for your primary pool filter. Reverse Osmosis filtration rates are much too slow to achieve a fast enough turnover rate to maintain a healthy pool. You would likely achieve a flow rate of roughly 50 GPH, and that is about 60x slower than what you need in an average-sized pool.

What they can do is filter out calcium from any water you use to fill up your pool. Once your calcium levels are correct, you can turn on that filter to keep the calcium levels from rising every time to top off your pool.

Switch from Calcium Hypochlorite

Cal-hypo can be a great sanitizer. However, if you have issues with maintaining consistent calcium levels, consider switching to a different sanitizer. Whenever you add this sanitizer to the pool, the sanitizing component is used, and the calcium is left behind. Since calcium does not evaporate, the calcium levels rise higher and higher.

How to Reduce High Levels of Calcium

Precipitate the Calcium and Bind with Flocculant

This method is super effective, but it comes with risks. Typically, you want to maintain a pH between 7.2 and 7.4, so the chlorine can do its job and calcium won’t precipitate into its solid scaling form. If we use this method, we will need to violate this rule temporarily. 

We need to raise the pH level to 8.2 or higher to encourage calcium scaling. However, instead of letting the calcium bind to the pool’s surface, we will give it a different target by using a flocculant. We use flocculants to clump certain substances together to make the contaminants large enough to be filtered.

When the calcium precipitates into its solid form, the pool will become cloudy. The flocculant will cling to the cloud of calcium and drop most of it to the floor. If you take a vacuum to it, you can remove that heavy calcium/flocculant combo.

You’ve got to be careful with this method because calcium scaling can stain the pool. This method actively encourages calcium scaling as part of the treatment. Ideally, the flocculant will bind with the calcium before the scaling has the opportunity to build.

When a sufficient amount of calcium has been vacuumed out of the pool, you can increase the acidity by lowering the pH.

Langelier Saturation Index 

Chemical reactions keep the world alive and your pool’s water in a constant state of transformation. One molecule transforms into another through the processes of isomerization (Reconfiguration) and dissociation. Some of these reactions can be reversed, and then the reversal can be reversed, and then it can be reversed again.

The forward transformation and the reversing transformation both have velocities to them. We can calculate those velocities when we measure the most important factors: concentration, pressure, and temperature. 

The velocities of these back-and-forth transformations will not be equal. In other words, the transformation from the original molecule might happen twice as often as the reversing transformation back into the original molecule.

If we leave the molecules alone and the factors are consistent, the transforming molecules will eventually settle into a persistent ratio. When the chemical reactions reach this persistent ratio, we call that state chemical equilibrium.

Your pool’s chemical balance is largely dependent upon maintaining these points of equilibrium, and a similar sense of equilibrium is found between calcium and hydrogen. Their proportions and resulting reactions will determine whether your pool is damaged from acidic etching or covered in calcium buildup. Where you land is denoted by a number on the Langelier Saturation Index which could be relabeled as “etching vs. scaling.”

The Langelier Saturation Index will help you to determine on which side of the etching vs. scaling line you happen to be. Ideally, you will have an index of zero where these two molecules cancel out their destructive impulses. However, maintaining a perfect balance upon this divide won’t be feasible, so acidic etching and calcium scaling will take place. It would be nice if we could simply filter them out, but they are necessary to the health of your pool.

The calcium in your pool is responsible for scaling, and the hydrogen in your pool wants to bind to nearby calcium. When the hydrogen can’t find enough calcium in the water, it will pull it out of the concrete. That is the corrosive process called etching 

If we balance these two molecules, we can use the hydrogen needed to bind to calcium to prevent the calcium from binding to the walls. However, if we want the calcium and hydrogen to easily balance and bind, we will need two things. First, we need the calcium to be accessible to the hydrogen, which means it should be soluble and dissolved. Two, we need just enough hydrogen to balance the pool chemicals, but nothing extra.


Calcium is water-soluble, but that solubility, like all soluble molecules, has a limit. When the water is saturated to those limits, anything beyond that is treated as insoluble and undissolved. Insoluble calcium forms calcium scaling.

The point of saturation starts at 0 on the Langelier Saturation Index and extends into the scaling side of the scale. We can change our point on that scale by making changes to any of the following list of factors:

  • Acidity (Hydrogen)
  • Alkalinity (Carbonate aka dissolved baking soda)
  • Water Hardness (Calcium)
  • Water Temperature
  • pH (Hydrogen)
  • Total Dissolved Solids (TDS)


Normally, if you have an accumulated substance that you wish to remove, hot water can help get rid of it. This is because warmer temperatures increase the solubility of most molecules. However, unlike most solids, increasing the temperature reduces calcium’s solubility. 

Heat actually facilitates calcium’s crystallization. That’s why you tend to see calcium deposits primarily around heat water heaters, chlorine generators, and warmed pipes. 

The example chart above shows how temperature affects calcium’s solubility. Keep in mind that this chart shows an incomplete picture since it focuses on the single factor of temperature.

pH and Alkalinity

A pool’s pH is a logarithmic value of the acidity of the water. Acids are hydrogen donators. When water is tested to be acidic, it means that there are a lot of these hydrogen donators in the water.

When a pool’s acidity is at the ideal level, we stabilize it with something alkaline. Most of the time, the alkaline substance will be baking soda (bicarbonate). 

pH and alkalinity can drastically change your pool’s place on the LSI scale. If you add too much acid, and it will quickly shift the LSI into the corrosive zone. Add too much baking soda, and calcium scaling will start to make a home in your pool. Take a look at the chart below to get a close approximation of how your pH and alkalinity will affect your LSI.

Total Dissolved Solids

Water can become overcrowded with chemicals and contaminants. As the various chemicals, yard debris, and human excretions proliferate the pool, the chemicals you add become increasingly ineffective. They get lost in the shuffle and don’t connect with your intended targets.

If your total dissolved solids are higher than the recommended for your pool type, you should take the time to drain your pool before you perform any other steps. In addition to increasing chemical effectiveness, this will also lower your calcium content. If you’re dealing with calcium scaling issues, this will likely be a good thing.

Environmental Factors That Affect pH And Hardness Levels

There are several conditions that can mitigate some of this mild calcium scale headache. Ultimately, how troublesome those scaling issues are will largely depend upon the answers to the following questions:

  • Does your city provide hard water?
  • Do you live in an area with frequent rainfall?
  • Is the rain acidic or base?
  • Do you have a pool heater or live in a warm climate?:

Let’s go over each one so that all of us can be on the same page.

Environmental Factor #1: Does Your City Provide Hard Water?

When water is described as soft or hard, those definitions are describing the mineral content of that water. Primarily, whether soft or hard, those minerals will be calcium and magnesium ions: bicarbonates, carbonates, chlorides, and sulfates. However, you will find other trace minerals as well.

The classifications for the levels of water hardness are described in Grains Per Gallon (GPG). The following table shows how each of those classifications is separated.

SoftModerateHardVery Hard
0 – 3.53.5 – 7.07.0 – 10.510.5 and up

When the water is harder, there is more calcium. More calcium means the pool becomes more prone to scaling. Unfortunately, every time you add water to the pool, it also adds calcium. Evaporation removes the water, but the calcium stays behind. Those levels will continually climb until you are forced to take action to lower those calcium levels.

The standard solution is to drain some of the pool’s water. Much of the free-floating calcium will go with the water. You won’t lower the water hardness to below the city tap levels, but it will be an improvement.

You can use chemical water softeners for a while, but you will need to eventually drain to keep your pool from being oversaturated by chemicals and minerals (A.K.A. Total Dissolved Solids). When oversaturated, pool chemicals become ineffective. 

Environmental Factor #2: Do You Live in an Area with Frequent Rainfall? Is It Highly Acidic?

When it comes to lowering your pool’s pH values, frequent rainfall might just be your best friend. Ideally, you want your pool’s pH value to stay around 7.2 to 7.4. The west side of the United States has “healthy” rain with a pH value of about 5. According to geological surveys, much of the east coast’s rain is considered very acidic due to the rating hovering around 4 for much of the territory.

Environmental Factor #3: Warm Temperatures: Pool Heaters and Warm Climates

Calcium scales are also more likely to form in warm and hot waters. Whether you are heating your pool artificially or you happen to live close to the equator, those warm waters will encourage calcium scales to form.

Water Hardness and Heat Sources

Water hardness refers to the mineral content of the water. The mineral content varies from location to location, so the water hardness of your local water supply will also change. If the local water supply delivers hard water, that indicates that the calcium content is significant. As calcium content increases, calcium scaling increases with it.

Common Questions About Pool Calcium Buildup

What Dissolves Calcium Fast?

You can choose from several products on the market, but you can also just use acid or mix up a water/acid solution. The important component is the acid, and you can find several acidic options in most homes. You’ll need something with a pH value sufficiently low enough to dissolve the calcium. Most pool owners have muriatic acid on hand, which works wonderfully to remove the calcium. When making that solution, keep the water/acid ratio in your mind. As you use more water, the pH value rises, and the acidity drops. 

pH Values 
Muriatic Acid: 1 to 2
Vinegar: 2.5
Citric Acid (Lemon): 2 to 3
Citric Acid (Orange): 3 to 4

What Is the White Stuff at the Bottom of the Pool?

There are a few likely possibilities, and it is usually easy enough to determine which one it is. First, if recently treated an algae issue, it might be dead algae that have turned white and dropped to the bottom of the pool. Second, did you or someone else recently add cyanuric acid to the pool? Cyanuric acid takes a day or two to dissolve, so it might be the remnants that still need to dissolve. Third, when calcium overtakes a pool, it can cover the pool’s floor in white calcium.

Does Vinegar Remove Calcium Deposits?

Vinegar is an acid, so it can dissolve calcium deposits as any other acid can. It has a pH nearly as low as muriatic acid and a pH value around 100,000 more acidic than the pool water ideal that prevents calcium buildup.

Many pool owners will mix water and vinegar, add it to a spray bottle, and scrub away the calcium buildup with a pool brush. Keep in mind that tap water has a 6+ pH. The more water you add, the higher the mixture’s pH will be, and the less effective it will be at removing the calcium.

Does Calcium Hardness Increaser Raise pH?

The answer depends on your pool’s current pH, but it shouldn’t be a problem. Calcium hardness increaser is made of calcium chloride, which has a pH value of 7.5. The ideal pool pH is between 7.2 and 7.4, so a slight pull to 7.5 should hardly affect a chemically balanced pool.

Will Low Calcium Hardness Cause Cloudy Pool?

Yes, it is possible. All of the chemicals need to be balanced, and too much or too little of any of them can result in a cloudy pool. Before adding any water hardness increaser, perform a chemical test to be sure that low calcium really is the cause.

The Pool Care Handbook & Video Course

by Swim University
This is an illustrated e-book with detailed videos and step-by-step instructions on how to best care for your swimming pool. 
© 2023 Pool Care Guide. All rights reserved.