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Is Soft Water Bad for Hot Tubs? (Yes, but here’s how to fix it)

By: Author Jeff Campbell

Posted on  - Last updated:

Categories Hot Tub Operational Tips

Soft water is the opposite of hard water, which means you have less calcium in the water, whereas hard water has a lot of calcium. But is soft water bad for hot tubs?

Soft water in a hot tub is bad and can lead to corrosion of the plumbing and equipment. But it can also cause an excess of foam in the hot tub’s water as well. Keep the calcium hardness between 180ppm to 200ppm to avoid issues with soft or hard water.

Alternately though, hard water that is high in calcium can leave scale residue on the shell and equipment and make the water cloudy.

It is important to know that soft water is just as bad as hard water, however, they do differ in the amount of calcium that they have in them.

So in this article, we’re looking at how to know how hard your water is. But more importantly, what to do to fix it! Continue reading on to learn more about soft and hard water issues with your hot tub.

Ready to Spend Less Time On Maintenance and More Time Enjoying Your Hot Tub?

Let’s face it. Balancing the water, cleaning filters, dealing with rashes, and trying to figure out which chemicals to buy and add can make you feel more like a chemist than someone who just wants to relax after a long hard day!

That’s exactly why The Hot Tub Handbook and Video Course is so valuable!

This is from Matt over at Swim University and he developed it for people looking to save money, time, and frustration. His tips on chemicals can save you $100/year just by making sure you buy only what you need.

So if you’re ready to stop being confused or frustrated with your hot tub and start spending more time in it, check out The Hot Tub Handbook and Video Course.

Just click that link to learn more on their website.

Is it OK to use soft water in a hot tub?

It is not OK to use soft water in a hot tub. The ideal water for a hot tub would be neither too soft nor too hard, with a calcium hardness between 180ppm to 200ppm.

But what is soft water?

Soft water is where you have little calcium in it. Never use soft water in your hot tub! If you do have to, you need to add something to increase the calcium hardness to prevent problems with your hot tub.

Such issues can be the following if you use soft water:

  • Corrosion to soft areas of the hot tub
  • Also, foaming issues can be a problem
  • Shiny areas of the hot tub will be corroded as well.

Make sure if your water is soft water, that you add calcium hardness increaser to get it up to at least 180 ppm.

My favorite calcium increaser is SpaGuard Spa Calcium Hardness Increaser (click to see it on Amazon).

It’s an Amazon’s Choice product, very inexpensive, and has almost 200 outstanding reviews. You only need 1 TBS to raise the calcium hardness by 25ppm. Eligible for free shipping!

CLICK HERE to see it on Amazon!

Only do this if it is 150ppm or less. At 180ppm, your hot tub will have the right balance in the water, protection for the surface of the hot tub, as well as making sure you do not have foaming issues.

You need to add the calcium hardness increaser every time you refill the hot tub with new water.

This is to keep the ppm balance correct and allows your hot tub to stay in great condition. Keep in mind, that soft water by itself is bad for your hot tub, just like hard water can end up being.

Is hard water bad for hot tubs?

Hard water is bad for hot tubs as it can leave scale residue on the shell and equipment, reducing the water flow and placing excess strain on the equipment. But it can also make the water cloudy.

But, what is hard water?

Hard water is where you have a lot of calcium in it. Never use hard water in your hot tub! If you do have to, you need to make sure you treat the water first.

Water that is too hard (too high in calcium) can cause scale deposits to build up in your pipes and equipment. It can also lead to cloudy water.

Also, make sure you keep your pH and alkalinity balanced as that affects how the calcium affects your water.

There are various ways you can treat hard water in your hot tub, including the following options:

  • Use a filtration system on your whole house (make sure it includes water from your hose)
    • Use a water softening system to reduce the calcium levels in your hard water.
    • You can also get a filter to do this for you, and it can screw right onto your backyard hose.
    • Just make sure you don’t make the water too soft as it leads to some of the other issues we discussed above.
  • Filter it out (requires cleaning or replacing your filter afterward) – great for extremely hard water
    • This way, you can combine the calcium to a pool chemical called CalTreat (click to see it on Amazon) that makes it into a larger particle that your filter system can remove.
    • This method takes 7-10 days to work, but can cut the calcium hardness by up to 200ppm. So this is best if you have really hard water
    • Then replace your hot tub filter with a new one or do a deep clean soak if your filter is still fairly new (CLICK HERE to see my favorite deep soak filter cleaner on Amazon)
  • Add a calcium reducer to your hot tub water (the easiest method)
    • You can find a chemical that controls calcium and other minerals by keeping them dissolved.
    • You can treat your hot tub weekly with this, after the first dose according to the instructions.
    • It can also dissolve scale deposits that already exist as well.

My favorite product to control water hardness, reduce scale, and prevent new scale buildup is by Leisure Time.

It’s called Defender (click to see the current price on Amazon) and it’s the perfect product if your water tends to be hard like my water. It has no reviews below 4-star, so you know this is a great product. Free shipping too!

CLICK HERE to see it on Amazon!

These are just a few of the ways you can control the calcium that comes from your hard water in your hot tub.

Keep in mind, hard water is usually over 180ppm. But hot tubs may be able to handle about 400ppm of calcium in it. However, anything over 400ppm can cause issues, such as cloudy water and scaling.

Can I put water softener salt in my hot tub?

Do not add water softener salt to a hot tub. Additionally, water filtered through a water softener system will be too soft in a hot tub. But water softener salt is not designed for hot tubs and high levels of salt in a hot tub can ruin the equipment over time.

But if you have extremely hard water it is natural to wonder if you can just add water softener salt to your hot tub to lower the calcium hardness.

There are a few problems with this. One is that if you’ve ever looked in the hopper of your water softener system’s salt tank, you know it can take weeks or months for the salt to disintegrate.

I don’t know about you, but I don’t want to be stepping on salt chunks every time I get in my hot tub.

But because it’s hard to know how much salt to add, you also risk softening the water too much. It’s far easier and simpler, and not much more expensive to use a product such as Leisure Time’s Defender (click to see the current price on Amazon).

That way you can not only lower the calcium hardness, but eliminate any current scale issues, and prevent future ones.


Ultimately there are a few reasons you might see cloudy water in your hot tub.

But, certainly, high calcium hardness could be one of those reasons! If you’re seeing that but aren’t sure it’s related to water hardness, check out this recent article to see all the possible reasons and solutions.

Just click that link to read it on my site.

How to harden soft water in a hot tub

For soft water in a hot tub, add a calcium hardness increaser to raise the calcium levels to 180ppm. Use a test strip designed to measure water hardness to determine that.

CLICK HERE to see my favorite calcium hardness increaser on Amazon.

If your garden hose has soft water in it instead of hard water, you will need to increase the calcium hardness to 180ppm in the water in your hot tub.

If you do not treat your soft water in your hot tub, it can cause issues later and permanently damage your hot tub and its components.

You need to apply a calcium hardness increaser to your soft hot tub water. My favorite one is SpaGuard Spa Calcium Hardness Increaser (click to see it on Amazon).

If you don’t treat the water, you can see the tile of your in-ground hot tub start to erode. The plaster surfaces can erode too. But even for portable hot tubs, the acrylic shell can get damaged too.

The hot tub floor, walls, and deck or concrete surfaces can start to become pitted. And the metallic parts of the hot tub will become corroded if you do not treat your soft water sooner rather than later.

Make sure to test your hot tub’s water calcium levels regularly. Ensure you do not dip below 150ppm or go over 200ppm. A hot tub can handle 400ppm for calcium and water hardness. However, it is best to keep it below that amount.

This is because of the chance of erosion and other issues that may arise if you accidentally go over 400ppm.

Keeping it between 180ppm to 200ppm is ideal for both soft and hard water usage in hot tubs. Always test your hot tub water for hardness, which is explained next.

How do I know how hard my water is?

Use a hot tub test strip that measures water hardness and match the color on the test strip after dipping in the water against the color chart on the side of the test strip package. Additionally, if white scale buildup is seen on showerheads in the house that is an indicator of hard water.

Again, you want the water in your hot tub to not be too soft or too hard.

Luckily, it’s easy to measure calcium levels with test strips and adjust the hardness up or down based on how hard the water is in your area.

But you can also use this handy chart I created to see how the water hardness tends to be for your area if you live in the USA:

If you live in one of the regions with hard or extremely hard water, you should definitely be testing your water. Then, use Leisure Time’s Defender (click to see the current price on Amazon) to reduce scale build-up and prevent future scale build-up.

If you live in a medium-hard area, you may not need to do anything, but I would probably still be checking.

But if you live in an area where the water is only a little hard, definitely check your water and consider using SpaGuard Spa Calcium Hardness Increaser (click to see it on Amazon) to increase the hardness to prevent corrosion.

Final thoughts!

Well, that was a lot of information about hard and soft water.

Bear in mind not all hot tub test strips check for water hardness.

Luckily, one from Leisure Time does! So CLICK HERE to get these inexpensive test strips on Amazon. They also check for pH, alkalinity, and chlorine/bromine.

This will help protect your hot tub and its components from corrosion before it starts! So, get those test kits, use those test strips, and check your water now.

Find out if you have hard or soft water and treat it according to this article. Then you can prevent any future corrosion issues and stop them before they start!

Ready to Spend Less Time On Maintenance and More Time Enjoying Your Hot Tub?

Let’s face it. Balancing the water, cleaning filters, dealing with rashes, and trying to figure out which chemicals to buy and add can make you feel more like a chemist than someone who just wants to relax after a long hard day!

That’s exactly why The Hot Tub Handbook and Video Course is so valuable!

This is from Matt over at Swim University and he developed it for people looking to save money, time, and frustration. His tips on chemicals can save you $100/year just by making sure you buy only what you need.

So if you’re ready to stop being confused or frustrated with your hot tub and start spending more time in it, check out The Hot Tub Handbook and Video Course.

Just click that link to learn more on their website.

Photos which require attribution:

Map of USA showing state names.png by User:Wapcaplet is licensed under CC3.0 and was modified by me showing data from the United States Geological Survey and 020 Calcium – Periodic Table of Elements by Science Activism is licensed under CC2.0

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Jeff Campbell
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