How To Reduce Calcium Hardness In a Spa Pool

Have you noticed that your spa water feels gritty, or observed white scaly flakes appearing around surfaces in your spa pool? This can be caused by calcium deposits which occur when your calcium hardness is too high.


Calcium hardness can affect the water quality and component life in your spa pool and surrounding areas if levels are not kept within the safe range.

But, what is calcium hardness exactly and why is keeping it balanced so important? Let’s dive straight into the deep end!

This article covers:

What is Calcium Hardness (Hard Water In Spa Pool)?

Calcium hardness refers to the level of calcium that is dissolved in your spa pool water.

It will vary depending on the calcium in your water source.

Rainwater bore water or river water will all have different levels of hardness.

Depending on where your water is sourced your calcium hardness will differ and needs to be adjusted accordingly.

Are Water Hardness and Calcium Hardness The Same Thing?

Just to clear things up from the start, calcium hardness and water hardness are the same things.

They are often used interchangeably to refer to the calcium levels in the water. If water is considered “soft” it means the calcium levels in the water are lower, and if it is considered “hard” then the calcium levels are higher.

It is worth noting that some measurements, like total hardness, refer to the combined levels of calcium and magnesium in the water. However, you can still work off of total hardness levels to balance water hardness effectively.

Back to top

Why is Water Hardness in a Spa Important?

Too much or too little calcium in your spa pool water can cause significant damage over time as calcium scale builds up inside your plumbing and around components in your spa like your jets.

A build-up of calcium scale can reduce the flow of water in your pipes and put extra pressure on your circulation pumps.

A high level of calcium can also cause cloudiness in your spa water.

This is why it is important to test and manage your water hardness and make sure it is balanced to avoid potential spa-ruining damage.

What Happens If The Water Is Too Hard?

Spa water that is too hard can be far more problematic long-term than water that is too soft. This is because the damage caused by high calcium levels in water can lead to more serious problems, including damage to the spa’s internal system.

When there is too much calcium in your spa pool water, calcium can start to build up in unseen places creating blockages and impeding water flow without you even realizing that it is happening.

Calcium can also build up along the spa shell, causing what is called scaling, which creates a rough surface that snags on bathing costumes and may cause water to go cloudy when the excess particles float around. Lastly, high calcium levels can affect the pH balance of your spa water, creating a higher risk for skin and eye irritation upon use.

Back to top

What Happens If The Water Is Too Soft?

Soft water is lacking calcium and will leach calcium from wherever it can to make up for the low levels. This means that the water will start to dissolve any surface or equipment that contains calcium such as plaster, grout, or concrete decking.

If water hardness is left unchecked for too long, low calcium levels can cause damage to the spa jets, heating elements, pool deck, and possibly the spa shell as these parts may contain traces of calcium. Lastly, low calcium in water can cause a slimy feel to the water and contribute to spa foam.

How To Measure Water Hardness/Calcium Hardness

To make sure your calcium hardness is at a safe level, you will need to measure it using some form of a test kit or test strips. The most common ways to test water hardness are:

1. Measure calcium hardness with a total hardness test strip

Total hardness measuring test strips are easier to use than any other method but are generally much less precise compared to other methods. These strips test the total hardness including the magnesium levels.

2. Measure calcium hardness with a liquid test kit

Liquid test kits are more manual than test strips but are often much more accurate and precise, as they can measure the calcium level on its own down to 10 ppm increments.

3. Take a sample of your water to a pool supply store

If testing your water hardness yourself is too daunting, you can take a sample of your water to your nearest spa pool supplier for a professional water test.

Back to top

How To Raise Water Hardness In A Spa Pool

Once your water has been tested and the results show a low water hardness, you can raise your water hardness by adding calcium to the water. Spa pools require a specific type of calcium called calcium chloride, which can be found in most calcium hardness increasers.

When you have your calcium hardness increaser ready, make sure to add the product very slowly as you don’t want to tilt the scale to the opposite end and come out with water that is now too hard. Hard water is more difficult to fix than soft water.

Pro tip: Do not add calcium chloride to your water shortly before or after adding soda ash or baking soda to the water or your water will become cloudy.

How To Lower Water Hardness In A spa pool

If your water hardness tests reveal high calcium levels in your water, you will most likely have to drain your water completely depending on the levels.

If your calcium levels are only a little higher than what they should be, then you can get away with draining and refilling only a little water from your spa pool and then adding a scale control product to the water on a weekly basis.

However, if your calcium hardness is far too high, then you will have to drain your water completely and clean out your spa pool before refilling. If your water source has naturally high calcium levels, refill your spa pool with a filter on your hose to keep out as much of the excess calcium as possible. Once full, you can use a scale control product to help keep your calcium levels balanced.

Back to top

Can I use a mineral softener in my spa?

Yes, the Zodiac® MagnaSpa™ mineral spa treatment is a mineral-based product that can also help soften your spa water, making it feel smoother.

Other Factors In Balancing Spa Water

Along with balancing calcium levels in your spa pool water, you need to take into account your pH balance, aka the water acidity, chlorine levels, and water temperature.

Keeping your water pH balanced is the most important, as this is ultimately what causes your water to be either corrosive or scaling and is affected by the other factors in spa pool water balancing.

Back to top

Spa Chemicals To Keep Your Spa Water Crystal Clear:

Depending on what type of spa system you have, you can add a variety of safe and effective spa chemicals to keep your water crystal clear. Both chlorine and saltwater spas use chlorine as their main anti-bacterial and spa sanitiser, but chlorine is not the only chemical you can consider.

Here is a list of chemicals you can keep handy to maintain a perfect spa pool:

  • Spa sanitiser
  • Spa shock
  • Defoamers
  • Scale control
  • PH adjusters

Back to top


Can I put water softener in a spa pool?

Yes, water softeners can be added to spa pools with high water hardness to lower the water hardness. However, if calcium levels are too high, it is better to drain the entire tub and refill the water with softened water.

How do I get rid of calcium in my spa pool without draining it?

You can keep calcium in your spa pool water at bay by draining a smaller amount of water out of the tub and using a scale control product upon refilling.

Does baking soda increase calcium hardness in a spa pool?

No, baking soda works with the pH balancing of spa pool water and does not increase calcium hardness. However, adding baking soda within several hours of adding calcium carbonate to water will cause water to turn cloudy and is not recommended.

Can I put CLR in my spa pool?

Yes, you can use CLR to remove scale from your spa pool. Simply use a 1:1 ratio of CLR to warm water and wipe onto the affected areas with a cloth. You can then scrub the scale off using a sponge or cloth.

Can you use baking soda in a spa pool?

Yes, you can use baking soda in a spa pool to help balance the pH of your spa pool water, especially if your pH balance and alkalinity are too low.

Got more questions?

Talk to us or email us your spa questions and we'll be happy to help!

Five Star Trust Pilot Rating

We are proud that Spa World customers have given us a Five Star Trustpilot rating.