Does your hot tub look like a giant bubble bath?

Then it’s time to learn what’s causing that foam, how to get rid of it and prevent it.

Foamy hot tub water is a common and unwelcome guest among hot tub owners. Several factors can cause it.

Foam in the hot tub happens, but FROG®, the water care expert, is here to help!

Causes of Foamy Hot Tub Water

Hot tub foam occurs when your hot tub’s water collides with air and surfactants. Surfactants are compounds that lower surface tension between a liquid and a gas.

When surfactants, water and air interact, a barrier forms between the water and air, resulting in hot tub foam.

As the amount of surfactants and air in your hot tub increase, so does bubble formation. When bubbles accumulate, they combine with each other and create foam.

What causes surfactant buildup?

You may be surprised. Some common things cause surfactant buildup and some you may not even know about. Once you know, you can manage them:

Hot tub with foam on the surface of the water

Oils and Lotions

Oils and lotions in the water are the most common causes of foamy hot tub water. Body oils, deodorant, beauty products, and body lotion can add a variety of surfactants to the water.

It’s the buildup over time that causes foam. And if the buildup isn’t treated, the surfactants these products add to the water lead to more and more foam.

Detergents and Soap

Detergent and soap residue on your bathing suits and skin inevitably get into your hot tub water when you get into your hot tub. These residues can cause foamy water.

We recommend you have a dedicated swimsuit to use in your hot tub – one that you don’t wash with detergent. After soaking in the hot tub, give swimsuits a good rinse and hang them to dry.

It’s also a good practice to rinse off with water – no soap – before entering your hot tub to get as much soap, oils and lotion residue off your skin as possible.

Close up shot of foamy hot tub water


Biofilm is a slimy and sticky microbial colony made up of different types of microorganisms including bacteria and algae.

These microbial growths attach themselves to hot tub surfaces. Biofilm develops when your hot tub water is not properly treated or maintained.

Biofilm can lead to foamy water because the bacteria within it produces surfactants as a byproduct of their metabolic processes.

Poor Water Balance

Poor water balance alone won’t cause foamy water. But poor water balance, especially low Total Hardness (also called calcium hardness), lowers the surface tension of water in the same way that surfactants do. When the water’s surface tension is lower, it is easier for it to combine with air, causing foam.

Underwater shot of water shooting out of the hot tub's jets

Foamy Water Solutions

Now that you know what causes foamy hot tub water, here’s how to solve it:

1. Balance Your Hot Tub Water

Even when it’s obvious that you have foamy hot tub water, it’s always best to start with balancing your water. Then you’ll know what needs adjusting.

Every time you balance your water, check these levels and correct as needed and in this order:

3 colored test strips sitting on a white towel in front of a lake
A graphic stating the ideal chemistry levels for hot tubs: Total Alkalinity at 80-120 ppm, pH at 7.2-7.6 and Total Hardness at 150-250 ppm

Want more details on water balancing? Download the FROG Water Balancing Guide for Hot Tubs here.

2. Shock the Hot Tub

If balancing the water didn’t get rid of the foam, the next step is to shock your hot tub water.

Hot tub shock oxidizes your hot tub’s water and reactivates your hot tub’s sanitizer. This oxidization helps break down surfactants and ultimately gets rid of foam.

FROG Maintain® is a non-chlorine shock that works in 15 minutes. It’s cyanuric acid free, so it won’t contribute to cyanuric acid buildup in hot tub water. Plus, it comes in a one dose cut-and-pour packet, so there’s no measuring and no mess. It’s easy!

3. Remove Buildup of Oils, Lotions, Detergents and Soap

If water balancing and shocking the water didn’t help get rid of foam, it’s time to remove any buildup from products that hot tub users have introduced to the water.

How? Add a scum absorber to the water! You’ll find numerous types of scum absorbers from sponges in fun shapes to scum balls. Check them out at your local retailer.

Once you put a scum absorber into the hot tub water, it will take a couple of days to fully absorb the scum.

However, you can speed up the process by adding multiple scum absorbers to the water. The foam should now recede unless biofilm is the cause.

Photo of the interior of a hot tub without any water in it.

4. Biofilm? Drain the Hot Tub

If absorbing the scum didn’t solve the problem, it is most likely that the hot tub foam is due to biofilm buildup.

The only way to get rid of foam due to biofilm buildup is to drain your hot tub and thoroughly clean the filter, surfaces, and pipes.

It can help to use a spa purge product prior to draining, it works inside the pipes. Then once the hot tub is drained, use a vinegar solution or a biofilm cleaner. Check with your local retailer for these products and follow manufacturer’s instructions when using a new product in your hot tub care routine.

5. Rinse it Out

Thoroughly clean and rinse the hot tub to ensure all the biofilm is gone – otherwise foam will return. Then, it’s time to refill the tub.

Important Tip: Put a hose filter on your hose when you fill your hot tub to avoid other damaging chemicals from entering the fresh water.

And also very important: After refilling, balance the water.

Once water is balanced, add your hot tub sanitizer.

Water Care Expert Tip:

Any type of defoamer or “anti-foam” product is only a short-term fix; it will remove the foam from the water temporarily. If you use an anti-foam product but don’t treat the water fully, the foam will return once the chemical has been used up. Foam is stubborn and best treated by the five steps outlined above!

And now, here’s 5 steps to prevent foam in your hot tub.

5 Steps to Prevent Foamy Hot Tub Water

1. Drain and Refill Your Hot Tub Regularly

Since foamy water is typically caused by buildup, it’s best to drain and refill your hot tub water regularly. You’ll find a lot of different recommendations on how often to drain your hot tub water, typically anytime from 2 to 3 months.

A man's hands holding a garden hose over a hot tub with water flowing out

However, those who use FROG® products can usually increase the time between draining as long as they replace the FROG Mineral Cartridge every 4 months. Note that the FROG Mineral Cartridge must be replaced every time you drain and refill the hot tub.

When you drain and refill your hot tub, consider it a refresh as it will get rid of dissolved solids that have accumulated in the water from hot tub use.

Once cleaned and refilled with water, balance the water before adding the sanitizer. Yes, balancing the water is one of they key parts to keeping the water clean, clear and ready when you are!

2. Use a Non-Chlorine Shock Weekly

Use a chlorine free shock weekly to prevent foamy hot tub water. Shocking the water helps break down oils and lotions or soap and detergent. If you use your hot tub frequently, more than 3 times a week, it’s a great idea to get on a consistent shocking schedule.

We recommend using FROG Maintain® – one dose in one single easy-to-pour pouch. Non-chlorine shock also means you get clean water without any Cyanuric Acid ever.

A man in a red t-shirt and blue overalls removes the hot tub's filter

3. Routinely Clean Your Filter

Clean the hot tub filter at least monthly. There’s an array of many products to choose from, including those to soak the filter in overnight or that you can hose off the next day. These cleaners remove all dirt, grease, soap, and oil buildup from the filter cartridge.

Another tip: Have an alternate clean filter cartridge ready to go to use while the “dirty” one is soaking.

This cycle not only helps you avoid hot tub problems, but also helps extend filter cartridge life. Avoiding trouble is better than fixing it!

4. Rinse off Before Taking a Soak

Take a quick shower before you use the hot tub. That helps prevent large amounts of products you may not even realize are on your skin or swimsuit from entering the water and disrupting the chemistry. Your favorite lotion, perfume, deodorant, sweat from the day, pollen, all kinds of “things” can be rinsed off with just plain water – no soap – and kept out of your hot tub water.

5. Have a Dedicated Swimsuit for Hot Tub Time

Bathing suits that have been washed with typical laundry are filled with detergent. Yes, even if you rinse them, soap residue remains. We recommend you choose a swimsuit that is not washed in a washing machine. Only rinse your selected suit with plain water and let it dry between uses.

Woman in spa turned to the back and looking at the camera as she cheers her champagne glass

The Foam Finale

Ultimately, foamy hot tub water can be a definite inconvenience for hot tub owners, but with the right knowledge and proper maintenance, you can easily manage and prevent it.

Now you know the various causes of foamy water, including the presence of oils, lotions, detergents, soap residues, and biofilm development. Most important, you know how to address that stubborn foamy water.

Implement preventive strategies and follow a consistent water care routine, then you can enjoy a crystal-clear and foam-free hot tub experience. Happy hot tubbing!


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