What Causes Foam in a Hot Tub? - Backyard Boss
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What Causes Foam in a Hot Tub?

Ever turn on your hot tub, walk away for a minute and come back to a tub of suds and bubbles? Well, you aren’t alone since hot tub foaming solutions is one of the most commonly searched for spa issue there is. Luckily, this seemingly large problem isn’t a large problem at all and is very easily remedied with a variety of different solutions.

Once you understand what causes foaming, you can take control of its introduction to your water to limit its source and use the proper products to eliminate it altogether. If you have been wondering what causes foam in a hot tub and need a solution, this is the article for you.

What is the Foam in a Hot Tub?

The technical explanation of what spa foam is, surrounds the agitation of water that has a concentration of total dissolved solid (TDS) built up. When they are mixed with air and water they act as a surfactant to reduce the surface tension of the water.

Shot of a beautiful young woman relaxing at the beauty spa.

But what does this mean exactly?

Detergent residue from your swimsuits, fabric softeners, dissolved salts, organic compounds, lotions, makeup, body oil, etc…are all rinsed into the water as dissolved solids. Even the best chemical treatment schedule leaves behind a little, and mixing them with air when the jets are on their surfactant properties create a foam.

This is due to surfactants having a molecular structure that allows one side to be attracted to water, and the other to repel water – so they organize themselves between this boundary of water and air: creating foam. The more TDS present, the more bubbles you will have due to their ability to stack upon each other.

Foaming Culprits and How to Avoid Them

There are some foaming culprits that are worse than others and reduce surface tension to create the perfect sudsy experience. Since you want to avoid this from happening, recognizing the reason you may have foam and applying the proper steps for eradication is a must.

Hot tub jets under water with bubles

Foreign Residues

These include the above mentioned detergents, lotions, beauty products, hair care products, sweat, body oils, dead skin cells, organic materials that may have blown into the water, etc… It also includes any beverages you may enjoy while soaking in the tub. Sugars and alcohol can both act as a surfactant.

What you can do:

These are the most common reasons for foam and also are the hardest to control. Rinsing your swimsuits through extra rinse cycles can help, as can rinsing off your body and hair before getting into the tub. Making sure you don’t spill your drink is also a must.

Low Calcium Levels

Low calcium makes your water ‘soft’ and weakens water surface tension. It also is very damaging to equipment in the long run so it is very important to keep your water calcium hardness levels where they belong.

What you can do:

Hardness test strips should be used weekly to measure these levels and water should be adjusted accordingly using calcium hardness increaser chemicals.

Overly High or Low pH Levels

Addition of a chemical to pH meter for measure the acidity of water in a swimming pool

Imbalanced water can also be a cause of a foamy spa experience. Many things can make your pH levels fluctuate, and treating the water on a regular maintenance schedule is an important start to keeping the water clear, clean, and in balance.

What you can do:

Test your water weekly using pH test strips, shock your water on a weekly schedule, and use pH increasers and decreasers as needed.

How to Get Rid of Hot Tub Foam

The above control suggestions are great ways to stay aware of why a hot tub may be foaming, plus how to initially avoid, or treat, the root cause. Of course, you aren’t going to know right away which of the above suggestions is the true culprit, or if you have a combination problem occuring. To narrow down your issue start simple:

First, Test Your Water

Service man checking chlorine, PH and other chemical levels in community pool

Test your pH, alkalinity, and sanitizer levels. These can give you a good indication if you have an imbalance causing your issue or something else. You also can test for TDS to allow you some insight into what you might be bringing into your spa each time you soak. Also, test for low calcium hardness.

Try adjusting these levels if you find them to be off and see if this isn’t your main culprit. It may take a few tries to test and add, which might have you consider a full tub drain.

Drain and Refill

If your water is especially foamy, you might want to just go ahead and drain the whole tub, clean it out, and refill. This allows you to start fresh having removed all surfacents and focus only on the chemical levels to start. Once you have refilled test your tub, added chemicals and allowed to sit, test your chemical levels again to check for low calcium or pH level fluctuations.

Don’t Use Inferior Chemicals

High quality products that have loyal consumer followings and reviews and come from trusted sources is what you want. Cheap options may not work as advertised and may include fillers or less active ingredients. You want those choices that are great for sanitizing and resetting imbalances, not a product simply looks good in a bottle.

Amazing equipment with chemical cleaning products and tools for the maintenance of the swimming pool on wooden surface against a nature background. Descent to the water. Close-up front view.

Use Anti-Foam Chemicals

If all of the above seems like a hassle, especially if you were looking forward to a good soak you do have a quick fix option. Foam removing chemicals work almost instantaneously and last for about 24 hours. They do not solve your problem at the source, but can turn around your initial experience and give you time to problem solve without screwing up your own plans.


If you have been struggling with the question of why your hot tub is foaming, you need to find the root cause and begin treatment to avoid unpleasant soaking experiences. Foam is caused by a few different culprits, but most commonly is due to too many dissolved solids bought into the water each time you soak. The great thing is, once you discover what is causing your issue, you can fix it!

If you have any questions or comments, or want to share what solutions have worked for you, please do so below. And, as always, please share!