What Causes Foam in a Hot Tub? How to Remove and Prevent It

  • By: John Parker
  • Last Updated: November 20, 2022

Hot tubs are supposed to have gentle rolling bubbles, but you are not supposed to have foamy hot tub water. Why does this happen? Is foam in a hot tub bad? Hot tubs are comfortable and fun until excess foam takes over. Hot tub foam can be removed and prevented from occurring again with a little care.

A foamy hot tub is normally caused by common surfactants such as soap, hair products, and human body residues. Depending on the surfactant type and the amount, the foam can become excessive. Fortunately, you can prevent and remove foams in hot tubs.

Perhaps a foamy hot tub looks like a bubble bath, but it is not as clean or safe as a regular tub. Foam in a hot tub is a clear sign that you need to clean your hot tub, and the faster you clean it, the better. Keep reading to find out why hot tubs foam, how to prevent the foam, and how to get rid of it.

what causes foam in a hot tub
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Why do hot tubs foam?

While a foaming hot tub might seem harmless, it can actually be a sign of some pretty nasty business. It may not be merely the relaxing bubble bath it looks like.

Hot tub foam is generally made out of three things:

  • Water
  • Air
  • Surfactants

While none of those elements are individually a problem, when they’re mixed with other residues, they create the foam that is a problem. The surfactants  (soap, oils, etc.) are the culprit when it comes to making a hot tub foam. Surfactants are molecules that are sticky by nature, lower liquid surface tension, and make it easier for oil-like substances to mix with water.

Now add in the air jets of a hot tub, and you get foams as a result. The jet pump is responsible for making tiny bubbles. With surfactants in the hot tub, however, the jet pump bubbles become covered in contaminants and are unable to pop which is why the foam persists. 

Water is the world’s greatest solvent. This means the water in your hot tub easily takes in all the chemicals and residues that enter it, and this includes surfactants. 

A well-maintained hot tub has spa water that is well mixed with calcium and sanitizing chemicals, which prevent foam. However, missing a few maintenance days or an excess amount of surfactants leads to foam build-up.

Below you will find the main surfactant sources.

Haircare productsHair products like shampoos, conditioners, hair gels, mousse, hair leave-in treatments, hair sprays, and so on are common surfactants in hot tubs.
Body/skin productsBody and face care products such as body lotions, body creams, deodorants, and body powders are surfactants that can cause foam in hot tubs. Make-up also acts as a surfactant in hot tub water.
Soaps & detergentsOur washed clothes tend to hold onto some soaps, bleach, detergents, and so on. The swimwear we wear has soaps and detergents that mix with the hot tub water.
DrinksSugary and fizzy drinks can spill into the hot tub, which creates the hot tub water to become imbalanced.
Low-quality
hot tub chemicals
Hot tub chemicals that are low in quality or used in excessive amounts can cause hot tub foam. This is why it is important to only use high-grade hot tub chemicals and also to use them in appropriate amounts.
The human bodyThe human body is obviously an unavoidable one, but the truth is the human body produces a lot of different things. Dead skin cells, fatty acids, and more are the human body’s byproducts. Nothing can be done about this, and it is why sanitizing chemicals and proper maintenance are important for hot tubs. 
Other dissolved substancesOther substances can interact with the hot tub water. Substances from the air, from nature, and so on and mix and react with the hot tub water. The total dissolved substances, if high, contributes to foaming.

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What Causes Foam in a Hot Tub? How to Remove and Prevent It 1

How to get rid of hot tub foam

As a long-term fix you can remove hot tub foam by replacing the water with clean, clear water. You can also use temporary chemical fixes to remove hot tub foam.

Test your hot tub water

Get the water tested. You need to know if the pH, alkalinity, and sanitizer levels are in optimal conditions or not. The test should also let you know about the total dissolved solids level, aka the surfactants, of your hot tub water.

You can get the water tested by taking a sample of it to a pool and hot tub store or use test strips.

Knowing the chemistry of your hot tub water will give you key insight into what specifically is causing your hot tub to foam.

Drain and refill your hot tub

The best way to remove the total dissolved substance is by draining your hot tub and refilling it again with clean water. If there is a very high amount of surfactants, then you should do a line flush too and get the filters replaced.

When your hot tub is completely drained, it is the perfect time to do a deep clean. You can wipe the hot tub interior down with a hot tub cleaner or a homemade vinegar-water mixture. Then wipe away all traces of the cleanser entirely, any residues left will cause future foam again.

Use anti-foam chemicals

You can purchase anti-foam products such as Pool & Spa Defoamer. This is a kind of chemical that gets rid of the foamy water quickly. This is a great fast option, especially if you want to use the hot tub soon and not go through the hassle of draining and refilling.

This anti-foam method should not be a substitute for draining and refilling. However, these chemicals do not address the root of the problem they merely keep foams away for up to 24 hours.

how to get rid of foam in hot tub

How to prevent foam in a hot tub

They say prevention is the best cure, and it applies to your hot tub too. They might seem extreme, but now that you know just what hot tub foam is, it’s worth going the extra mile to prevent hot tub foam from occurring in the first place.

Here are some common rules or guidelines to follow if you have a hot tub.

  • Everyone should shower beforehand
    You and anyone else who goes into the hot tub should shower beforehand. This is to wash off makeup, body oils, soap residue or cream residue, and other chemicals from the body.
  • Pre-rinse bathing suits
    The bathing suits of anyone entering the hot tub, if worn, should be well cleaned and well rinsed with fresh water. This will make sure any extra chemicals such as bleach, laundry detergent, fabric softeners, and so forth are washed out and do not enter the hot tub.
  • Do not let your head go underwater
    This is especially important for those who have long hair. Additionally, those with long hair should tie their hair up in a high bun. It is even better if you wear a cap or hat to keep the hair out of the water. Beards, especially long beards, should also not be dipped into the water.
  • Invest in quality hot tub chemicals
    Only purchase and use good quality chemicals. Ideally, buy hot tub chemicals from trusted brands.
  • No eating or drinking in hot tubs
    Try not to eat and drink in the hot tub. Eating and drinking always come with the chance of spilling, which is not good for the hot tub.
  • Regularly clean your hot tub
    Proper and timely maintenance is very important to prevent hot tub foam. Regularly drain out and clean your hot tub. You should change hot tub water at least once every few months.
  • Clean hot tub filters
    Make sure you clean your hot tub filter or filters if you have more than one regularly. They will be less effective if dirty. Although you can give them just a quick rinse with a garden hose you should give them a thorough clean at least once a month. Read How to clean hot tub filters.

Is foam in a hot tub harmful?

It is not the end of the world if your hot tub has foam in it. However, a foamy hot tub can mean it is not sanitized properly. In some rare cases, hot tub foam can be pathogenic. To avoid any risks, only enter your hot tub when it is clear of foam.

Foam in your hot tub

Milky-colored water and foam in a hot tub is a clear indication that the chemical balance of the water is not right. This will only get worse with time unless you treat it. This is not only bad for you, but with time this is also bad for the hot tub itself. The walls will corrode and discolor.

Sometimes the water foam is also caused by bacteria build-up. This is called a biofilm which can be detrimental to both you and your hot tub. That is why you should test your hot tub water regularly and add whatever chemicals such as chlorine or bromine to keep it balanced.

Foam in public hot tubs

Public hot tubs and spas are more likely to have high levels of foam in them. Commercialized hot tubs, even with foam, might look cozy at first, but you should be wary because it probably indicates unsanitized water. It is probably a better idea to skip foamy public spas, or at least take a good shower straight afterward.

Conclusion

You want your soaks in the hot tub to take away your worries, not add to them!

Now you know what causes foam in hot tubs. After reading this, you should know what to do next time your hot tub starts to foam. Remember that prevention is key, so do your best to prevent any contaminants from going into your hot tub.

Happy soaking.