How to fix foamy hot tub water

Posted by Nick Clamp in Maintaining a Hot Tub Guides on 27th March 2022

Just opened up your hot tub’s cover to find a thick layer of foam?

Don’t worry – your hot tub isn’t broken, but you are going to need to get rid of that foam before you can get in it.

Read on to find out how to fix foamy hot tub water – and prevent it from ever happening again.

How to fix foamy hot tub water – fast

Got people coming over and need a fix for your foamy hot tub now? The quickest fix is to add a foam remover chemical, which will get rid of the foam sitting on your hot tub in minutes and stop it from building up again for the rest of the day.

While this is a handy solution if you’re in a pinch, it only treats the symptom, not the cause. It’s an effective temporary solution, but it’s only a band aid. Read on to find out why there’s foam in your hot tub in the first place and how to prevent it from happening again.

What causes foamy hot tub water?

Foamy hot tub water all comes down to surfactants – molecules that reduce the surface tension of water and make it easier for oils and water to mix. 

The total dissolved solids (TDS) your hot tub test strip measures? Those are surfactants. And if they build up in your spa, they’ll form a film on its surface that traps air and forms bubbles. Add your hot tub’s jets into the mix and you get bubbles – lots of them. 

And that’s how you get foam in your hot tub.

Where surfactants come from

You can prevent hot tub foam by stopping surfactants from building up in your spa in the first place. That means maintaining good hot tub chemistry so your sanitiser can do its job of dissolving organic compounds so they don’t build up.

But no matter how hard you try, there’s always going to be some surfactants in your hot tub’s water. The key is to always keep that amount down to a manageable level.

With that in mind, things to keep a keen eye on include:

Soap, shampoo, and detergents

You leave any residual soap from your skin, shampoo from your hair, and detergent from your swimming costume behind when you get out of your spa. Each of these is a surfactant that can cause hot tub foam if left unchecked.

Oils and lotions

Suntan lotion, make-up, deodorant, and moisturiser can all build up over time and cause hot tub foam.

Food and drink

Sitting back and sipping a cold drink during a soak in your home spa is one of life’s greatest pleasures. But beware: spilled drinks and food crumbs will send your TDS levels through the roof, which will quickly lead to hot tub foam if left untreated. Avoid this by shocking your hot tub if you ever spill a drink in it.

© Hot Tub House Yorkshire

People

It’s not exactly pleasant to think about, but the truth is that you leave oils and dead skin cells behind every time you get out of your hot tub. Keep your sanitiser levels topped up and these will all get dissolved. But if you have lots of people round for a dip in your tub, the standard dose of sanitiser probably won’t be strong enough to neutralise everything your guests leave behind. So, be sure to shock your hot tub after each time you entertain to give it a sanitiser boost that will prevent surfactants from building up and foam from forming.

Dirt and debris

Your sanitiser will go into overdrive to try and break down dead leaves and muck that gets brought into your spa on the bottom of feet. So, be sure to scoop any dirt and debris out of your tub as soon as you spot it so your sanitiser doesn’t get used up trying to break that down rather than neutralising the compounds that cause hot tub foam.

Unbalanced hot tub chemistry

Unbalanced hot tub chemistry won’t cause foamy hot tub water by itself. But poor water balance – especially low calcium hardness – prevents your sanitiser from working effectively and reduces the surface tension of your hot tub’s water. Together, these make your hot tub a lot more likely to foam up.

Cheap hot tub chemicals

Cheap hot tub chemicals can lead to a whole host of problems with keeping your hot tub’s water balanced. Stick to quality spa chemicals to keep the chances of hot tub foam to a minimum and   make sure you spend as much time enjoying your hot tub – and as little correcting its chemical levels – as possible.

How to get rid of foam in a hot tub

A foam remover chemical will quickly – but only temporarily – remove the foam for your hot tub. To get rid of it for good, follow these simple steps: 

1. Test your water

The first thing you should do with a foamy hot tub is test its water. Once you know which of the pH, alkalinity, sanitizer, calcium hardness, and total dissolved solids levels are out of balance you’ll know what to keep an eye on in the future to help make sure it doesn’t happen again.

If your hot tub’s chemistry is totally unbalanced across the board, your best bet is usually emptying, cleaning, and refilling your spa (more on that in just a bit).

If they’re not too bad – and your hot tub isn’t too foamy – it can be worth adjusting your hot tub’s chemicals and seeing if that does the trick. Pay special attention to the calcium hardness and TDS levels if you choose to go this route, as these are the most common causes of a foamy hot tub.

2. Shock your spa

Hot tub shock oxidises your hot tub’s water and reactivates the chlorine or bromine in its water. This will help it break down surfactants and get rid of foam, making it a great next line of defence if rebalancing your hot tub’s chemicals doesn’t do the trick. 

If your hot tub is foaming, its sanitiser levels are more than likely running low. A chlorine-based hot tub shock will boost its sanitiser levels as well as oxidise the water, hitting two birds with one stone.

3. Drain, clean, and refill your hot tub

If shocking your spa doesn’t work – or if your hot tub’s water is so unbalanced that you don’t think it’s worth trying to rescue – draining your hot tub and starting again is a surefire way of getting rid of the foam.

Follow these simple steps to empty your hot tub and make sure no contaminants are left behind that might make it foam up again:

  1. ‘Zap’ the water with a fast-acting plumbing cleaner to remove any residue or greasy body oils from the inside of the plumbing system, then drain your hot tub’s water.
  2. Once empty, thoroughly clean the inside of your hot tub with a damp cloth and a spa surface cleaner solution.
  3. Remove your hot tub’s filters and soak them in chemical cleaner, then rinse them off.
  4. Remove your hot tub’s headrests and thoroughly clean them (and the acrylic area behind them) to remove any potential contaminants. Once dry, use a vinyl protectant such as 303 Protectant to help preserve their lifespan.
  5. Start refilling your hot tub, then add some fast-acting chlorine or bromine granules to start the sanitisation process. Remember that you’re aiming for a Free Chlorine level of 2 – 5mg/l or a Total Bromine level of 3 – 6mg/l once the spa is refilled, so don’t go overboard at this stage with your chemical levels.
  6. Once your spa is full, check and adjust pH to 7.2 – 7.6 and Total Alkalinity (TA) to 125 – 150mg/l.
  7. If your hot tub cover is made of vinyl, wash it with warm soapy water, leave it to dry, then use 303 Protectant to protect it from UV damage and prolong its lifespan.

Once your hot tub is full of fresh water, test the water and leave it to circulate for at least a day. Then test it again and adjust if necessary before you hop in.

© Artesian Spas

How to prevent foamy hot tub water

You can prevent your hot tub from foaming up by:

  • Showering and removing make-up before you get in your hot tub so you don’t bring dirt, sweat, lotions, deodorants, or cosmetics in with you.
  • Wash your swimsuit separately, using less detergent and giving them an extra rinse cycle before drying them.
  • Keep a close eye on your hot tub’s water balance – particularly the calcium hardness and TDS levels.
  • Refresh your hot tub’s water every three months as part of your regular hot tub maintenance routine.
  • Shock your spa after each time you have a lot of people in at once.
  • Use water clarifier, which helps remove organic compounds from your spa’s water.
  • Get a hot tub with a first-class filtration system, which will remove as many surfactants as possible.

The final word

No matter what you do, surfactants are going to slowly build up in your hot tub – which is why you need to change its water every three months. Stick to the advice we’ve laid out in this short guide and compounds won’t build up to the point they cause foamy hot tub water. And if they ever do, you now know exactly how to fix it – and prevent it from happening again.

For more hot tub maintenance tips – plus our pick of the best hot tubs on the market today for every budget – get the latest edition of WhatSpa? magazine for free.

About the author

Nick Clamp

I am the Editor-in-Chief at WhatSpa? Media Group and my job is to keep you informed about the very latest hot tubs on the UK market... the best job in the world! When I'm not being deluged with press releases and hot tub brochures I enjoy keeping fit and participating in endurance events including triathlons and distance running.

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