How to Balance Calcium Hardness in Your Pool

Updated Jun 1, 2021

Calcium Hardness is a blessing and a curse when it comes to managing your pool chemistry. Most of us are stuck with hard water from the get-go just because we live in cities with terrible water purification systems.


But, we have put together a comprehensive guide to help you navigate the water hardness situation and keep your pool as perfect as can be year-round.

What is Calcium Hardness?

Calcium hardness is the measurement of how hard or soft the water is in your pool. Hardness is the combination of calcium and magnesium particulates that are dissolved in your water. The ideal range for calcium hardness is between 150ppm – 400ppm.

Low Calcium Hardness

So, what happens if the water becomes, “too soft”? Yes, that is a thing! If the levels get too low, i.e. under 150ppm, your water becomes corrosive and can erode the tile grout and even start stripping your plaster surfaces.

You will even see pitting or etching starting to form on surfaces, such as stone or pool decking around any metal. So, look near pipes, ladders, lights, filters, etc.

The reason this happens is because the water naturally has a need for a specific range of calcium hardness and will try to balance itself out by taking it from whatever it touches. This means, it will pull the calcium from any connecting stonework, concrete, metals, grout, or whatever else may have calcium in it. That is what causes the destruction of those items.

How to Raise Calcium Hardness

This is pretty simple these days… just find yourself any calcium hardness increaser from the local retailer and dose according to its recommendations for your pool size.

High Calcium Hardness

High Calcium Hardness, AKA, “Hard Water” is in just about everyone’s home. 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 hardness 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.

People might tell you the only option is to drain the pool if your water’s calcium 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.”

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 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:

calcium hardness in united states

Calcium Hardness 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”), unless you happen to have a Smart Chemistry system setup. These systems can handle calcium harness issues so they don’t get out of control.

Calcium Hardness can Damage your Pool and Equipment

So, if you don’t stay on top of your calcium hardness, 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 to Lower Calcium Hardness

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). If you already have a pool filled with hard water, just drain some of the water and refill using this filter to dilute the TDS until you reach the desired calcium hardness levels.

Clarifier and Flocculant Wont Work

Your traditional options for removing particulates in the water, such as Clarifier and Flocculant, are not going to handle calcium hardness like you think. They are meant to clump together the free and floating particulates in your water, but if the calcium is dissolved, they won’t do anything.

So, the next best method for lowering calcium hardness, is by isolating the calcium. Now, when we say isolate the calcium, we are referring to dissolved calcium.

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.

Use a Sequestering Agent to Remove Calcium

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. 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.

Use a Chelation Agent to Disable Calcium

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.


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. Be sure to use the pre-fill filter when diluting.


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 calcium hardness and not let hard water affect your awesome pool.