Why do Pools form Calcium Scale?

Updated Jun 1, 2021

Calcium Scale tends to form in the hottest water first… and secondly, it will tend to form where the water has the least amount of circulation. And, finally, if you have hard water, you will need to pay more attention to management. So, if you live in hot weather Cities, or you have hard water, you need to pay attention to this.


So how do you know if you have Hard Water?

Well, 85% of the United States has hard water, so it’s pretty darn common.

Especially, if you live in these Top 10 Cities

One grain per gallon (gpg) is equivalent to 17.14 parts per million (ppm).

City Grains/ Gallon Hardness (PPM)
Indianapolis, IN 19.9 341
Jacksonville, FL 24 410.9
Kansas City, MO 8.3 142
Las Vegas, NV 16.5 282.5
Minneapolis, MN 26.4 453
Phoenix, AZ 14.1 241.5
Salt Lake City, UT 13 222.8
San Antonio, TX 16 273.9
San Jose, CA 18.6 320
Tampa, FL 17.5 300

* Those are yearly averages.

The most common reason you see calcium scale in pools is that just about every city in the United States has hard water, which can range up to more than 400 ppm, which is the top of the recommended range.

There are plenty of calcium and magnesium particulates in the water to begin with, allowing for the potential to start forming scale if your chemistry gets out of whack. So, just in case you don’t have a Smart Chemistry system already, here is everything you need to know to manage hard water in our pool.

What Causes Calcium Scale to Form?

  • Your pool’s water Alkalinity is too high
  • Your pool’s water pH is too high
  • Your pool’s water temperature gets too high.

People might tell you the only option is to drain the pool if your hardness reads over 400 ppm, but it’s not necessarily the case. You can control these issues, even if you have the highest range of hard water.

For example, in the city of Minneapolis, the water measures 453 ppm right out of the hose, so draining is obviously not going to be the answer, because you literally just filled the pool. That being said…

Calcium Hardness Range for Pools

For reference, any water measured with over 3.5 grains of calcium and magnesium bicarbonates per gallon is deemed “hard water.”

We recommend having calcium hardness between 150-400 ppm

Some cities have hard water that borders or exceeds the top of the recommended range right from the start, so be aware of your city water calcium hardness levels to better prepare yourself on how to handle things.

To give you some reference points, we have measured hardness variations across multiple cities, and you can see below that they are all so very different:

Hard Water in Every City in United States

Calcium will build up over time and start messing with your pool chemistry.

Calcium also reacts with hot weather and tends to create an ugly ring around your pool tiles called, “scale” which builds up over time.

Luckily, it’s not an immediate issue that you have to worry about. It is a long-term process which means every 2-3 years, you will need to drain and refill your pool water to remove those total dissolved solids (“TDS”).

Calcium Scale can Damage your Pool and Equipment.

So, if you don’t stay on top of your hard water, it can quickly get out of hand and you will start seeing:

  1. Waterline on Tiles
  2. Scale Forming inside your Saltwater Generators (Salt Cells)
  3. Scale Forming inside your Pool Heater
  4. Cloudy Water

How do I Remove Waterline Calcium Scale from the Tiles on my Pool?

A simple brushing or wiping of those tiles from time to time should keep the scale from getting out of hand.

Dipping the brush or sponge in muriatic acid will instantly dissolve that scale but be sure to wear gloves and mask to avoid fumes and skin contact.

How do I Remove Calcium Scale from the Salt Cell on my Pool?

Typically, scale will be inside saltwater chlorine generators (salt cells), or heat exchangers, or the top of your water line on your pool tiles, rock features, or vinyl.

Salt chlorine generators, AKA (“Salt Cells”) use a process called electrolysis to generate chlorine from sodium chloride (salt). This process involves electricity, which creates heat and a very high pH.

Most pool owners tend to shut off their pool pumps and salt cells at the same time. This will basically create the perfect storm of scale potential in the salt cell with high pH, no circulation and hot water.

Once scale forms, the salt cell loses its effectiveness, and the lifespan gets significantly reduced. Calcium buildup is one of the biggest challenges with saltwater pools. Solution…

Run your pool pump 30 minutes after the salt cell turns off to flush it out and avoid scale formation.

We highly recommend you inspect your salt cell every 3 months and clean it with a muriatic acid. This will keep your salt cell operating at maximum capacity, while extending its life expectancy as long as possible.

How do I Remove Calcium Scale from the Inside of my Pool Heater?

Scaling is an especially problematic for pools with heaters because the scale will build up quickly as it moves through the heater’s plumbing. Over time, the calcium in the heater’s plumbing will build up and cause the heater to fail. So, it’s important to keep on top of your pool heater maintenance.

Pro Tip…

Run your pool pump 30 minutes after the heater turns off to flush it out and avoid scale formation.

Now, besides the above-mentioned tips… if your water chemistry is balanced properly, it will help reduce the formation of scale and keep things manageable for you.

How do I Remove Calcium Scale from My Pool?

Pre-Fill Filter

To start, prior to filling up your pool, you can use a pre-fill filter on your hose to catch as much of the fine grain particular matter that adds to the total dissolved solids, or (TDS).

Keep pH in Check

Since calcium tends to enjoy a high pH, it scales as the pH rises, so be sure to maintain a range under 7.8 at least. Most recommendations fall between 7.2 to 7.8. Muriatic Acid is a great way to fight high pH. It’s also a great way to fight any scale formation if you start seeing any.

Isolate the Calcium

Now, when we say isolate the calcium, we are referring to dissolved calcium. That means your traditional options for removing particulates in the water, such as Clarifier and Flocculant, are not going to handle things.

There are two methods of chemical additives that can be used to combat the calcium buildup in your pool water… Sequestering Agent and Chelation Agent.

1) Sequestering Agent

Sequestering agents draw metals into itself and binds those metals into a clump. Calcium is technically considered a metal, so it reacts in the same way. So, when the calcium attaches to the sequestering agent, all the metal’s ions are essentially no longer able to oxidize or stain. It basically becomes unable to form the calcium scale you know and love, and prevents waterlines, dust, cloudiness, etc. When this clumping is done, it makes it easier for your pool filter to catch the clumps and remove them from the water. Sequestering agents are typically used for removing calcium.

2) Chelation Agent

Chelation does a similar reaction with metals, but it does it in a different way. Instead of clumping everything together, with multiple ions, it only binds with the calcium ions and isolates them individually. Because the chelation process binds with individual ions, it makes it harder to filter out of the pool, since there are no clumps to catch. Chelation essentially renders the calcium helpless as it relates to forming scale. It keeps it in check and will just remain in the water without causing the reaction that leads to scale.

Both have their pros and cons, and require a little more effort after use, but they are both solid applications to prevent calcium scale.  We also created a quick image for you to see the difference in the ion binding between the two options.

Image of chelation-vs-sequestering-agents

Reverse Osmosis

Reverse osmosis, sometimes referred to as (“RO”) is an innovative water purification process that uses a membrane filtration technology that works by forcing water under pressure through very tiny pores of a semi-permeable membrane. This process is a little overboard, expensive and typically requires a massive truck or machine to do your pool. RO machines are usually used at water treatment facilities.


One of the easiest methods of controlling total dissolved solids (“TDS”), is to drain and refill your pool water every so often. Keeping the dilution going throughout the year, with incremental drain/refills, will be more manageable than full drain/refill every 2-3 years.

Acid Wash

There are also two forms of acid washing…

Simple Acid Wash

If you want to avoid the cost and effort of a major acid wash job, our first recommendation is to do simple acid washing with your pool. This basically means you get your protective gloves and goggles and mask, brush and sponge, and you basically go around the pool’s waterline.

Start with brushing the wall or tiles with the brush and water… then, take your sponge, dip it in muriatic acid and slowly work your way around the pool with simple circle movements.

You won’t have to scrub very hard at all. Muriatic acid will instantly start dissolving any basic scale build-up if any is there.

This should keep your waterline looking pristine for years if you do this annually or twice a year, if possible.

Full Acid Wash

If you have neglected the pool or inherited a pool from someone who has not kept up on things, and you have extreme scaling everywhere, then, a full acid wash is the way to go.

Acid washing essentially strips a very thin layer of plaster off your pool wall to get things looking nice and clean. Luckily, you wont have to do a full acid wash that often, as it takes years for neglect on a pool to get to the point of needing a full acid wash.


Anyways, we hope this article was useful. We have been maintaining pools for some time now and found that the above recommendations should keep you on the right track with managing your hard water pool and avoid calcium scale.

Sick of doing your own Pool Maintenance?

Staying on top of pool maintenance is a process and time-consuming for sure.

It can also add up to a lot of wasted time and money if you don’t keep on top of scheduled maintenance.

Wouldn’t it be great if someone created a device that you could plug-in to your pool and it just took care of everything?

Wait, there is? Um, yes there sure is!

Smart Chemistry May Be a Better Solution for You

If you want to get a pretty amazing and affordable pool automation system, you can always try Smart Chemistry, and save time and money pretty darn quick.

Yes, we know it’s a seamless plug, but we believe in our product so much, we give it a lifetime guarantee and you can cancel anytime.


It even controls your pool water chemistry too!

You won’t have to deal with pool test kits, pool test strips, or a test of any kind anymore! Imagine that!

All starting at $9.99!

We also have a lowest cost chemical guarantee, so you won’t find a cheaper option… even if you DIY.

Yes, it’s crazy, but true. Smart Chemistry is the future of pools!

Bonus Tip…

So, stop wasting your life googling your swimming pool degree and start deciding where to put the insane amount of money and time we are going to save you with Smart Chemistry.

It’s time to get your life back!

We are Luv2Swim and it’s time to get this pool party started!


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