Calcium Hardness for Pool


What is calcium hardness?

Calcium hardness is simply a measure of how hard or soft your pool water is.

Calcium is a mineral that’s found in most water sources and it often combines with other minerals such as magnesium, which results in water hardness. Too much of minerals in your pool water can cause deposits and buildups.

In other words, if you have hard water, it means there’s high calcium content in your pool water.

There are two types of hardness measurements for your pool water: total calcium hardness and total hardness.

Total calcium hardness is a measurement of calcium hardness in your pool. On the other hand, total hardness measures calcium and magnesium level in your pool.

Ideal calcium hardness level

Generally speaking, the ideal range for calcium hardness is between 150 to 400 ppm.

More specifically, these are the ideal calcium hardness level for different pool types.

  • Plaster pool: 200 to 400 ppm
  • Vinyl pool: 80 to 150 ppm
  • Fiberglass pool: 150 to 250 ppm

As a pool owner, you need to proactively manage the calcium hardness level to keep your pool safe from potential damage.

What happens if the calcium hardness level is too low?

It’s important to keep a balanced level of calcium in your pool.

If the level is too low, it can cause issues such as:

  • Damage to your plaster and decking
  • Staining of pool surface
  • Heater damage
  • Grout damage

When your pool calcium hardness level is too low, then the water in your pool will try to extract calcium from whatever it can. Any part of your pool that contains calcium, such as concrete decks and stone, becomes vulnerable to damages from your pool water.

It’s hard to reverse the damage that has already taken place, so it’s best to prevent it in the first place.

What happens if the calcium hardness level is too high?

If the level of calcium hardness is too high, it can cause:

  • Scaling of pool surface
  • Scale buildup on your tile line and the plaster
  • Clogged filter and heater
  • Cloudy water
  • Clogged pipes

If you have a high level of calcium in your pool water, it also means you will have an oversaturation of dissolved particles. This increases the likelihood of damage to your pool equipment by blocking the flow of your pool water.

How often to test calcium hardness level?

You want to test calcium hardness in your pool once a month, at least. Frequent testing will allow you to make necessary adjustments before your pool incurs damage.

It’s normal for your test result to have a slight fluctuation from month to month due to differences in weather and the level of other chemicals in your pool.

How to measure calcium hardness in your pool

Test strips, such as Aquacheck 7 allows you to measure the total hardness, which includes magnesium, in your pool.

Alternatively, you can use a drop-count titration method to get an accurate measurement of calcium hardness level.

If you don’t have a test kit, I suggest you go to the local pool store with your pool water to get it tested.

What is a calcium hardness increaser?

A calcium hardness increaser is a chemical that you add to your swimming pool when your pool has a low level of calcium hardness. If the calcium hardness level for your pool starts to dip below 150 ppm, you’d want to consider adding an increaser.

How to lower calcium hardness in pool

When you fill your pool water for the first time, you want to test your water for calcium hardness. 

Whatever calcium hardness level you get at that point in time is the calcium hardness that will stay with your pool.

In places like Florida, the water hardness is 250 ppm. In other places, that level can be as high as 300 to 500 ppm. If you are filling your pool with water that’s already hard, then the calcium hardness of your pool water will naturally be high.

Unless you employ some fancy, expensive filtration process, such as a reverse osmosis system, to filter calcium out of your pool water, there isn’t much you can do to lower calcium hardness.

So, assuming your pool is filled with fresh water, changing your water isn’t going to reduce calcium hardness since the level is pre-determined by your water source.

That said, when your calcium hardness level increases over time, you can reset it to the original level by draining and refilling your pool water with fresh water.

Additionally, you can keep the calcium hardness level in your pool under control by not using calcium-based products, such as cal-hypo, in your pool.

How to increase calcium hardness in your pool if the level is too low

The easiest way to raise the calcium hardness level in your pool is by adding a calcium hardness increaser, such as calcium chloride, to your swimming pool.

Your product should come with a label that shows how much you need to add depending on your pool size.

Precautions when handling calcium chloride

Calcium chloride gets very hot when added to water, so there are some precautions you need to take before handling calcium chloride.

  • Use a bucket when pouring calcium chloride into your pool water
  • Avoid adding more than 10 pounds of calcium chloride at a time to reduce the risk of burning
  • Too much calcium can melt a plastic bucket
  • Always add calcium to the water, not the other way around
  • Make sure to use safety goggles and gloves

Specific instructions

  1. Put on your safety gear
  2. Fill your bucket halfway with water
  3. Add calcium to water and stir the water until the calcium is dissolved
  4. Give some time until your calcium mixture cools down a little. Pouring hot mixture into your pool can sometimes harm the surface
  5. Pour the calcium mixture into your pool water while the pump is running

One tip I’d like to give you is to add a portion and test for the calcium hardness level before adding the rest of your calcium chloride.

You want to avoid the mistake of adding too much because the only way to lower your pool’s calcium hardness level to its baseline is by draining and re-filling your pool with fresh water.

How to prevent scaling from calcium hardness

Although it’s difficult to lower the calcium hardness level in your pool, you can prevent most of the scaling by keeping your pool pH and alkalinity at an optimal level.

You want to keep your pool pH at around 7 to 7.4 and alkalinity at about 80 ppm

For lowering your pool pH, you can use muriatic acid.

Does baking soda cause calcium hardness?

Baking soda is often used to raise the pH and alkalinity of pools.

But if you use too much baking soda, it can lead to a build-up of calcium and cause scaling on your pool surface, which can give problems to your pool filters. 


Although it’s a bit of a hassle to manage your pool calcium level, it’s an essential component of increasing the longevity of your pool.

If you are ever unsure of anything, I highly recommend you talk to a pool specialist.

Good luck!

Leave a Reply

Your email address will not be published. Required fields are marked *