Is Soft Water Bad for Hot Tubs?

By Calvin | Last Updated: May 29, 2021 | Maintenance / Water Chemistry

There is usually a lot of concern when it comes to filling your hot tub with water. Like you already don’t have enough on your plate by worrying about the contaminants in the water, now you have to worry about the nature of the water too. Many hot tub owners worry if soft water is bad for hot tubs, here is what I discovered:

Soft water is bad for hot tubs. Using soft water in hot tubs can cause corrosion and foam in the water. This is because there is a very low level of calcium and other minerals in the water.

But that’s just the quick snapshot. Let’s take a closer look. But first, what do we mean by soft water? Let’s find out.

Buying a hot tub is easy, maintaining a clean hot tub is hard. You have to deal with different chemicals to keep the hot tub clean. Except for chemicals you have to deal with water type. There are two types-- soft and hard water. That got me thinking, is soft water bad for your hot tub? Yes, it is. But you can harden it a little to make it perfect.

What is Soft Water?

Soft water refers to a water source or water body that has a very low level of calcium in it. Soft water doesn’t mean water that is soft in terms of texture. Soft water means the water is soft in terms of its mineral content. It is the opposite of hard water.

Hard water refers to a water source or water body that has a high level of calcium, iron, dissolved metals, and minerals in it. The presence of these minerals and iron in high levels makes the water hard. When these minerals are absent in the water, the water is considered soft.

Many hot tub users tend to be confused when they discover that soft water isn’t good for hot tubs. This is because hard water isn’t good for hot tubs either. When the water is hard, the iron and mineral deposit inside the water will cause scale build-up on the shell of the hot tub.

The irons like calcium and magnesium will also react harshly to the sanitizers that are added to the water in the tub. This harsh reaction causes green water and brown tint on the waterline.

So here is the million-dollar question. If hard water is bad for hot tubs and soft water is also bad for hot tubs, what nature of water is good for hot tubs? Well, the answer to that is below.

Related Read >>> How To Convert To a Salt Water Hot Tub?

Why Is Soft Water Bad for Hot Tubs?

Soft water is bad for hot tubs because it has a low level of calcium and this makes the water very aggressive. If the calcium and mineral levels in the water are very low, the water will become under-saturated.

This means the water doesn’t have all the properties it should have and the water will therefore become very aggressive in a bid to obtain the calcium that it needs.

Think of soft water like a zombie. Only that this zombie is not interested in blood, it is constantly in search of calcium. This means the metal parts of your hot tub aren’t safe with soft water in the tub.

Soft Water Can Cause Corrosion

Soft water can cause corrosion to the metal parts of your hot tub. These include the circulation pump, the jets, the shell of the hot tub, and the likes. Soft water also leads to foaming in the hot tub.

If you use soft water with a low ppm in your hot tub then that can cause corrosion.

Since the calcium levels are low, the water look will appear foamy when you turn on the jets. The glossy parts of your hot tub will also become very dull and corroded with soft water in the hot tub.

Soft Water Can Cause Etching

Soft water can also cause etching. Etching is a process where the water in the tub starts to eat away at materials that contain calcium.

This is usually not a problem since the frame of the hot tub doesn’t contain calcium but this can be a very big problem if your hot tub base or foundation was made from concrete.

Related Read >>> How To Convert To a Salt Water Hot Tub?

Soft Water Can Damage The Concrete Base

Concrete paste has a lot of calcium in it. When you splash the water or drain it and it falls on the concrete basement, the soft water will start to eat away at the concrete foundation.

This can cause the hot tub to become unbalanced. This small issue can damage the frame of your hot tub and that will cost a lot of cash to fix.

Now you know that soft water is bad for your hot tub. But how can you tell you have soft water in the hot tub and how can you increase the hardness of soft water? Keep reading to find out.

Related Read >>> Do Hot Tubs Need a Concrete Base?

What Type of Water Is Good for Hot Tubs?

The ideal nature of water for hot tubs and spas is neither soft nor hard water. The ideal nature of water is a mixture of both. The water has to be between hard water and soft water.

There are two types of water-- hard and soft water. So, what type of water is good for hot tubs? The best water for your hot tub should have 80-200ppm. That means neither hard nor soft water is good for your hot tub. The water "between" hard and soft is the best.

For hot tubs and spas, soft water has a ppm (parts per million) rating between 10ppm and 50ppm. This is usually too low for hot tubs and can cause corrosion.

Hard water has a ppm rating between 150ppm and 250ppm. This is usually too high for hot tubs and can cause scale buildup on the shell.

The right level of water hardness for hot tubs is between 80ppm and 200ppm. Any rating above or below this range means the hardness of your hot tub water is way off and you should expect to have problems with the hot tub.

On average, the best level of hardness for hot tub water is about 180ppm. If the calcium level is measured at 180ppm, then you have nothing to worry about. But why is soft water bad for hot tubs?

Related Read >>> Do Hot Tubs Lose Water?

How Do I Know if the Water Is Soft?

To know if the water is hard or soft, you have to test it. Though there are a few signs that can indicate you have soft water in the hot tub but these signs are not the most accurate because they can be caused by other factors.

For instance, corrosion on the metal parts of the hot tub can be caused by soft water but it can also be caused by too many chemicals. So the best way to be sure you have soft water is to test the water.

To test the water, you can buy a water testing kit like a digital tester or test strips. Any of these will tell you how soft or hard the water is and it will also indicate if you need to lower or increase the hardness of the water.

Another alternative is to investigate your water source. You can ask the water supply company in your area for the calcium readings of the water that is supplied. If you live in areas where the water supplied is soft water, then chances are you will have soft water in the hot tub too.

If the result of the test shows that the water is soft, then you will need to increase the hardness of the water. How do you do that? Let’s find out.

How to Harden Soft Water in a Hot Tub?

If you have tested the water in the hot tub and you are sure you have soft water in there, you can increase the hardness of the water by adding calcium increaser to the water.

Different products can be used to increase the hardness of the water in the hot tub. They are known as calcium increaser or calcium hardness increaser. You can get such products at your local pool store.

Use Calcium Increaser

When you get the calcium increaser, you need to add it to the water in the hot tub by following the manufacturer’s instructions.

If your hot tub water is soft, then you have use a calcium increase to increase the ppm levels and to harden the water.

Some products are so potent that can increase the water hardness by 30ppm by adding just one tablespoon of the said product. So follow the instructions so you don’t end up with water hardness that will be too hard.

Turn on the Jets

As an expert tip, while adding the calcium hardness increaser to the water, ensure that the jets are running so that the water is well circulated and the calcium increaser is well absorbed in the water.

If the calcium increaser comes in a powdery form which by the way most of them do, you might want to mix the required quantity with some water first before adding it to the water in the hot tub.

Now you know how to harden soft water, but how do you soften hard water?

How to Soften Hard Water in the Hot Tub

If the water in the hot tub is too hard (over 200ppm), then you need to reduce it. Luckily, this can be done in many ways.

Use a Hose Filter

First, always use a hose filter when filling the hot tub. If hard water is what you are trying to prevent, you can do so by using a hose filter.

A hose filter will prevent the bulk of the irons and other minerals that get into the hot tub when you are filling it. It will also block off any debris that may flow into the water.

You can also reduce the calcium levels by treating the water weekly. Just be mindful of the chemicals you use because the irons in the hard water don’t react well to sanitizers.

Related Read >>> Chlorine vs Salt Water Hot Tubs?

Use Calcium Reducer

Another alternative is to use a water softener or calcium reducer. This will help to reduce the calcium levels in the water. If you have extremely hard water in the hot tub, like 400ppm and above, you can add water softener salt to the water in the hot tub but there is a slight twist.

While the salt will reduce the water hardness, it can take days and even weeks for the salt to fully dissolve in the water. This means you can be picking salt particles out of your hot tub for weeks. So go easy on the water softener salt.

Overall, soft water is very bad for your hot tub so stay away from soft water. But if that’s all you have, ensure to add a calcium hardness increaser to the water so it doesn’t damage your hot tub.

So there you have it. Ensure to leave a comment below if you found this post helpful. You can also check out other posts on this website for more hot tub tips. Have a nice day.

Hi, I'm Calvin Hall, the owner of Hot Tub Wiki. I worked at a local Spa Service for a few years before creating this website. I have owned several hot tubs and fixed a thousand of them. So, I know a thing or two about hot tubs.