What Causes a Hot Tub to Foam?

Michael Keenan


Hot Tub Troubleshooting

Are you wondering why your hot tub is foaming? If your hot tub is full of white sudsy bubbles then it’s time to investigate what could be causing it. It could be something as simple as too much soap or oil left behind from your body or clothes, or something bigger like high levels of total dissolved solids (TDS) coming from the water supply source.

The interaction of these elements with the water and air creates a layer of soapy bubbles that float to the surface.

I’ll take a look at all these possible causes – from surfactants and chemical balancers to biological contaminants – so you can better understand what is making your hot tub foam up.

Plus, If you want to know how to get rid of hot tub foam – and stop it happening again – I have a full guide here.

what causes hot tub to foam

Quick Answer:

Foaming in hot tubs is caused by a combination of elements, including surfactants, chemical balancers, total dissolved solids (TDS), biological contaminants, and aeration from the jets present.

These interact with the water and air to form a layer of white soapy bubbles. To get rid of foam in your hot tub, check out my article for more information.

Overview of Foaming in Hot Tubs

Whenever the surface tension of the water in hot tubs decreases when in contact with other liquids, solids, or gases, foam is the natural outcome. Thus, there is an interplay between water, air, and substances known as surfactants.

Surfactants are the main reasons behind the low surface tension in the water. Usually, some surfactants are already a part of your hot tubs, but external products added to the hot tub are usually what increase the chances of foam in the tub.

They result in the formation of a layer between the water and the air, which manifests in the form of foam.

Learn more about calcium flakes in your hot tub and how to get rid of them.

Causes of Hot Tub Foaming

Foaming occurring in hot tubs is common enough due to external substances that you might not worry about it too much. However, there are times when the foam may point to another issue or cause that you should first become aware of before figuring out how to remove it.

Go through the following points to understand some causes of hot tub foaming.

Excessive Amounts of Surfactants

If you tend to use body oils, lotions, and soaps often inside your hot tub, this could well explain why there is foam in the hot tub. Each of these acts as a surfactant, resulting in multiple bubbles and foamy white layers on the water. Some surfactants left behind on your body or clothes may also result in foam.

Overuse of Chemical Balancers

It is common for the water in your hot tub to undergo changes in its chemistry, such as its pH level increasing too much or the calcium level reducing. If you keep using too many chemical balancers without confirming their quality and efficacy, this might result in foam.

I have a range of articles and guides covering everything you need to know about using different hot tub chemicals – properly! Check them out:

oily residue on water

High Levels of Total Dissolved Solids (TDS)

Total dissolved solids (TDS) refer to the combination of organic and inorganic elements that might be present in the water in your hot tub. Examples include salts, minerals, waste materials, and lots more.

This typically comes from the water supply source, which is why it can help to have filters in place.

Biological Contaminants

Biological contaminants, such as algae or bacteria, may also be present in the water. Bacteria usually enter the water through your own body or other substances like food, dirt, and debris while algae are commonly formed due to still water.

These can alter the water chemistry and increase the surfactants in the hot tub.

Aeration from the Jets or Waterfalls

Hot tubs usually come installed with jets or waterfalls that help circulate heated water throughout the structure. The strength of the pressure from these jets circulates lots of air through the water, causing it to foam up.

The presence of additional surfactants may further end up increasing the total amount of foam that forms on the surface.

excess foam

Final Remarks

Knowing what causes a hot tub to foam will help you figure out how to remove it safely and effectively. From external substances like body oils, lotions, and soaps acting as surfactants to biological contaminants altering water chemistry – these are all elements that could lead to a layer of white soapy bubbles being formed on top of your hot tub water.

Luckily enough, it is possible to get rid of this kind of foam. You can check out my article on how you can get rid of foam in a hot tub for more information.


Is foam in a hot tub dangerous for your health?

Foam in a hot tub is not directly dangerous to your health. It can be an indicator of water quality problems which left unchecked could have potential health issues.

Are there any negative effects associated with foaming in hot tubs?

While there are no serious negative effects associated with foaming, too much foam can make it harder to enjoy your hot tub experience as it will reduce visibility and create an oily film on top of the water’s surface.

What causes excess foaming in a hot tub?

Excess foaming in hot tubs is usually caused by oils, body lotions, detergents, and other organic materials that can accumulate on the surface of the water over time.

How can I prevent foaming in my hot tub?

To prevent foaming, you should check your filter regularly for any dirt or debris that may be causing an excess of suds in your hot tub. You could also use a chemical foam suppressant to help keep foam levels down.

michael keenan author

Author - Michael Keenan

I'm Michael Keenan the owner and creator of the Outdoor Care Guide. I'm a trained horticulturist with over 30 years of experience in pool care, plant care, and landscape care! Seemed like a good idea to share - I think I can make your life easier and save you some time and money!