What Causes Foam in a Hot Tub? (How to Prevent & Fix)


Excessive foam is fairly common among new hot tub owners. As long as you deal with the problem right away, it’s nothing to be concerned about. So what’s caused this foamy surprise?

The causes of foam in a hot tub include beauty products, cleaning detergents, low calcium hardness, natural oils in human skin, food, and drink. Foam appears when the water is no longer fresh and the pH isn’t properly balanced with sanitizing chemicals.

When it comes to a foamy hot tub, I’ve been there and got the t-shirt, so I’m going to show you:

  • Why it happens
  • How harmful it is
  • How to prevent it
  • How to get rid of it

Why do I get foam in my hot tub?

To understand why foam forms in a hot tub, you need to know what surfactants and water surface tension are. The good news is that I’m going to make it super simple.

  • Surfactants are “impurities” that reduce surface tension in water.
  • Reduced surface tension is what allows high-density objects such as insects (and bubbles) to float without being submerged.

With proper maintenance to water chemistry, sanitizers neutralize any surfactants in the water. This prevents foam from forming and floating on the surface of the water.

You want to keep your water as clean and fresh as possible. But every time you use your spa, you introduce more surfactants (impurities).

Over time, spa water becomes resistant to chemicals, meaning that they no longer have any sanitizing effects. This is why water needs to be drained and refilled at least every 4 months.

So what are these troublesome surfactants that cause excessive foam in hot tubs?

Personal care products

Products such as moisturizers, shampoo, conditioner, deodorants, perfumes, hairspray, and makeup are full of oils and other ingredients that you don’t want mixing with your hot tub water.

Residual soap or phosphates from the laundry detergent used to wash your swimsuit also cause foam to build up.

Your body

Your body is full of natural oils, dead skin cells, and sweat that wreaks havoc with your water chemistry. And don’t even think about peeing in your hot tub.

Low calcium hardness

Low calcium hardness is found in soft water and can make it easier for foam to form on the surface of the water because it decreases the water surface tension.

Food and drink

Perhaps you like to enjoy a few nibbles accompanied by a glass of wine, beer, or even a cocktail with your soak. I’m not judging.

But unfortunately, accidentally spilling your drink results in a chemical imbalance that causes foam to soon appear.

Is foam in a hot tub harmful?

At first glance, a hot tub full of foam may look quite inviting. You might think it’s like taking a huge, relaxing bubble bath. But is foamy hot tub water safe?

Hot tub foam is not usually harmful to your health, but it does cause damage to your hot tub. Foam is caused by a chemical imbalance in the water and should be remedied as soon as possible to prevent any parts from corroding, as well as discoloration to the hot tub shell walls.

No amount of foam is normal in a hot tub, and the foam will not go away on its own. If your hot tub keeps foaming up, it’s a sign that the water is too old or that there aren’t enough sanitizing chemicals present.

And although the foam isn’t likely to cause any health issues, I’m sure the last thing you want is to be bathing in everyone else’s gunk.

Make sure to remedy the situation as soon as possible to avoid expensive repairs to both the spa shell and any susceptible mechanical components.

How to prevent hot tub foam

By being proactive, you can greatly reduce the risk of foamy water.

  1. Take a shower before getting into the hot tub to reduce the amount of oils and dead skin on your body. Clean off any beauty products and rinse the soap residue off thoroughly.
  2. Don’t wash swimwear in the washing machine. Rinse using hot water to avoid introducing laundry detergent into the spa.
  3. Don’t introduce shampoos and other hair care products by putting your head under the water. If you have long hair, tie it up or wear a cap.
  4. Do not fill the hot tub with softened water.
  5. Use a calcium hardness increaser to raise the calcium levels if you live in a soft-water area.
  6. Don’t eat or drink in the hot tub to prevent accidents.
  7. Use spa shock on a weekly basis to break down impurities and oxidize the water.
  8. Open the hot tub cover at least once a week to introduce oxygen.
  9. Perform a regular water maintenance routine. Use water test strips and adjust chemicals accordingly.
  10. Don’t buy cheap chemicals. Investing in known brands will save you money in the long run.
  11. Drain and clean your hot tub at least every 4 months.

Neglecting your spa maintenance routine for just a few days can allow a build-up that leads to foamy water.

Foam caused by low calcium water is of particular concern as it can lead to corrosion in parts and fittings. Because the water is starved of calcium, it tries to source it from the metal components in your hot tub.

Use this calcium hardness increaserOpens in a new tab. if the levels are low. Make sure to keep your hot tub covered as rain or snow will also lower the calcium levels.

When it comes to food and drink, the last thing I want to be is a kill-joy. Soaking in my hot tub with a glass of fizz pretending to be Beyoncé for 20 minutes a day is probably as close as I’ll ever get.

That’s why it’s such a good idea to mount a swivel drinks trayOpens in a new tab. to the side of the tub so you have somewhere to put your drink down between selfies sips.

Back to reality. There’s a good chance of foam appearing after a party with lots of bathers. If that’s the case, then don’t worry. A foamy hot tub is an easy fix.

How do you get rid of foam in a hot tub?

There are several ways of dealing with excessive hot tub foam, from quick fixes to a full drain and refill. Just make sure that you don’t try to save a few pennies by using cheap chemicals.

Just like with washing-up liquid, you get what you pay for. Pricer chemicals are more concentrated, meaning you ned to use less.

What’s more, cheap chemicals can even cause a build-up of surfactants, which means you’ll have to spend extra on corrective treatments. Crazy, right?

The quick-fix

If you don’t have time to drain and refill your hot tub (around 36 hours’ work), you can get rid of the foam for up to 24 hours by using this foam removerOpens in a new tab. by Leisure Time.

It’s compatible with chlorine, bromine, ozone, and biguanide sanitizers and gets to work immediately. You’ll only need to wait 15 minutes before getting back into your foam-free hot tub.

While defoamers are great in a pinch, they don’t address the underlying cause of the issue. To do that, you’ll need to clean the plumbing and fully drain all of the water.

Full drain and refill

Draining all of the water from your hot tub is the only way to ensure that the foam doesn’t return. But before you drain the water, there are a few things to do first.

Test your water

Use a water testing kitOpens in a new tab. (more precise) or test stripsOpens in a new tab. (less precise) to find out the levels of pH, alkalinity, sanitizer, and TDS. Having these readings will better help you to understand how to avoid the problem in the future.

If you live in an area with soft water, it’s a good idea to test for calcium hardness levels too.

Line flush

Before you go pulling the plug, this is the perfect time to carry out a full line flush of the hot tub’s plumbing.

Even with correct levels of sanitizers, a hot tub can develop biofilm, which is a breeding ground for bacteria.

Bacteria in the water can expose you to dangers such as Legionnaires’ disease, E. coli, and hot tub folliculitis.

Unfortunately, the build-up can’t be removed through normal water circulation, filtration, or by adding extra sanitizers or shock.

The only way to remove the bacteria build-up is by using this line flush cleanerOpens in a new tab..

Add the line cleaner and allow it to run for a couple of hours. As the water circulates, don’t be alarmed by the horrible-looking scum that forms on the water’s surface.

The scum means it’s getting to work, ridding the pipes of all that nasty biofilm. With that out the way, we can move on to draining the water.

Drain and refill

Turn off all power to your hot tub and drain using a hose or sump pumpOpens in a new tab.. Remove the filters and give them a thorough clean using this filter cleanerOpens in a new tab..

If no amount of cleaning can get the filters looking like new, you need to replace themOpens in a new tab..

Once empty, wipe down the inside of your empty hot tub using a special hot tub cleanerOpens in a new tab. or a mixture of 1 part distilled white vinegar to 4 parts water.

Make sure to rinse the hot tub thoroughly, ensuring that it is completely dry. If you don’t remove the cleaner and standing water, the foam will just come back.

I like to use this inexpensive wet/dry vacOpens in a new tab. for the remaining water that’s left behind in the seats and footwells. It saves so much time and is far less exhausting than doing it by hand. Whereas drying with a cloth just moves dust and debris around, my wet/dry vac is far more efficient at sucking up all of the rubbish sitting in the water.

Now it’s time to fill the spa back up with fresh, clean water. To minimize introducing impurities during fill-up, attach this hose filterOpens in a new tab. to your garden hose.

Once filled, add the necessary chemicals and allow them to circulate for at least 24 hours. Once circulation is complete, test the water to make sure it’s safe to soak in.

Taking the time to clean out the plumbing, drain all of the water, and thoroughly clean the hot tub will make sure the water is foam-free after refilling. Keep on top of your water maintenance routine and be proactive about reducing impurities in the water.

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