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

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?

Here’s what I’ve learned in owning 4 hot tubs:

While hard water that is high in calcium can leave scale residue on the shell and equipment and make the water cloudy, soft water can lead to corrosion of your plumbing and equipment. Keep the calcium hardness between 180ppm to 200ppm to avoid issues with soft or hard water.

But that’s just the basics!

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.

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

No is the short answer. 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?

Again, yes. 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?

Generally speaking, adding salt of any kind (especially Epsom or bath) is not a good idea.

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

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?

The million-dollar question!

To find out if you have hard water, just check your sinks in the kitchen and bathroom. See a white scale on them?, Then you probably have hard water scale in your pipes as well.

This can end up in your hot tub too and is a quick way to determine if you have hard water.

However, there are other ways to test the water specifically to know its hardness levels. You can do this by buying a test kit and using test strips in your hot tub water.

It will tell you what your calcium hardness levels are. And that will help you determine if you need to act and fix the water issues with the steps mentioned above.

It is best to do this when you first get your hot tub, or even before you buy one.

This way you will be able to reduce any issues with your hot tub that hard or soft water can cause. That way your hot tub will not get corroded or have corrosion issues with its components.

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.

Did I cover all you wanted to know about hot tubs and soft water?

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!


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

Jeff Campbell

Jeff Campbell is a husband, father, martial artist, budget-master, Disney-addict, musician, hot tub lover, and recovering foodie having spent over 2 decades as a leader for Whole Foods Market.

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