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How To Prevent and Remove Hot Tub Scum

Matt Giovanisci, Founder and CEO of Swim University By Matt Giovanisci | November 3, 2020

It’s one thing to see plain ol’ dirt and debris in your hot tub. It happens, especially if your spa is located outside. But it’s a whole other ballgame when you find yourself dealing with hot tub scum. Blech.

Look, we all slack on our chores from time to time. But even if you’ve been diligent about keeping your hot tub clean, it may still develop oily scum on the water, or a scum ring around the shell. The key is to know what causes it so you can remove it and keep it from happening again.

What Causes Hot Tub Scum?

Some of what goes into hot tub water is filtered out. Dust, debris, chemicals, even bacteria, depending on the type of filter you have. But a filter can only do so much, and only for so long.

If the contaminants that end up in your hot tub are left long enough, or you haven’t taken measures to combat them, they’ll eventually form a layer of hot tub scum that floats on the surface of the water, or forms a nasty ring around the hot tub shell.

Bodily Residue

This is the most common cause of hot tub scum. Every day, our bodies slough off 30,000 to 40,000 dead skin cells, and the top 18 to 23 layers of our skin are made up of dead cells lining up to be expelled. That process is sped up by sitting in hot, bubbly water.

We also lose between 50 and 100 hairs a day, and our bodies produce oils that rise to the surface of our skin. Plus, even though you’re sitting in water, it’s usually much higher than your body temperature, which means you may sweat while you soak.

The minute you step into your hot tub, a lot of those contaminants end up in the water with you.

Personal Care Products

In addition to the things our bodies naturally shed each day, we add a lot of products. Deodorant, shampoo, perfume, lotion, anything and everything you use every to make yourself look, smell, and feel good goes right into the water if you don’t remove it all beforehand.


We don’t mean getting into your spa with your jewelry on. We’re talking about metal present in the water.

All water has at least some amount of metals like copper, iron, and magnesium. Depending on where you live, the concentrations may be higher in your city-supplied water, and possibly even higher if you use well water.

Once those metals start reacting with chlorine, they can oxidize and stain the shell. But they can also cause a greenish hot tub scum to form in the water.

Note: Speaking of jewelry in hot tubs, that’s not a good idea. Silver will have a chemical reaction with chlorine that will create a tarnish that regular jewelry cleaner won’t remove. Gold is a soft metal that can also be damaged by chlorine, and soft stones like pearls and turquoise can be damaged beyond repair. To protect your jewelry from damage and yourself from heartache, always remove it before getting into a hot tub (or a pool, for that matter).

Poor Water Chemistry

Keeping your water balanced is essential to keeping your hot tub clean and anyone who soaks in it healthy. Unbalanced water—specifically, high pH—can create a welcoming environment for algae, bacteria, and hot tub scum.

Dirty or Worn Out Filter

Your filter’s job is to keep the hot tub water clean. It can’t very well do its job if it’s dirty. And at some point, cleaning the filter won’t be enough to keep it functioning properly, and you’ll need to replace it.

Until you either clean or replace your filter, all those nasty things that cause hot tub scum will just pass right through the filter that can no longer capture them, and end up right back in the water.

Hot Tub Scum Types

Knowing what might cause the formation of hot tub scum is only half the battle. Its color will tell what did cause it so you’ll know how to get rid of it.

Brown Scum

If the water’s pH level is too high, it can cause minerals like iron to react with the chlorine. This will create a nasty brown scum on the water’s surface, and it may also stick to the shell’s surface.

Green Scum

You’ve seen what happens to an old penny, right? It turns green. So if you see green scum in your hot tub, it’s likely you have a high copper level in the water. Magnesium in the water will also cause this reaction.

Blue-Green Scum

This is the big bad of hot tub scum. It’s caused by a combination of several things: metals, bodily secretions, and personal care products in the water, and a dirty or worn-out filter. Put all those things together, and you’ve got blue-green scum.

Important: If you see white flakes in your hot tub, they’re probably calcium scale deposits. And if you notice a white, non-flaky substance floating on the water or attached to the shell’s surface, you probably have white water mold in your hot tub. Those two problems need to be addressed a little differently, so make sure you know what you’re dealing with before you start the removal and treatment process.

How to Prevent Hot Tub Scum

The type of scum you have in your hot tub will determine how you prevent it.

Brown Scum Prevention

This one’s an easy fix. Since brown scum is caused by too-high pH levels, first, keep the water balanced. Second, if the pH level gets higher than 7.6, use a pH decreaser to bring it down to the correct range.

Green Scum Prevention

You can’t keep metals out of your water completely, but you can keep them from messing up your hot tub.

Use a hose filter when filling your hot tub. It’ll keep a portion of the dissolved metals (as well as other nasty stuff you’d rather not soak in) out of the water so you’re starting with cleaner, fresher water.

Also, keep a metal sequestrant on hand. This doesn’t remove metals, but clumps them together so they can be grabbed by the filter before they have a chance to oxidize and form that green hot tub scum, or worse, stain your spa.

As a bonus, some metal sequestrants also address scaling caused by high calcium hardness, so if that’s something you’re also concerned about, look for one hot tub chemical that does both.

Blue-Green Scum Prevention

Metals, bodily secretions, and toiletries, oh my! Throw in a bad filter for good measure.

To keep metals under control, follow the same preventive measures you’d follow for green scum. For the rest, several general steps will help you prevent blue-green and any other type of hot tub scum.

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Test the Water Regularly

How are you going to know whether the pH is too high, or that you have a high level of dissolved metals in your water source? By testing the water.

You can do this with test strips or a liquid testing kit. Any of them will test for pH, but you may need to find special strips to test for metals if that’s a concern.

Test the water at least weekly, but more often if you’re having trouble with hot tub scum, your water has high metal content, or you use your spa often.

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Shower Before Using Your Hot Tub

All those loose hairs and body oils? A quick rinse can help keep them out of your hot tub water. But the lotions, perfumes, makeup, and deodorants? The only way those are coming off is in a full shower with soap.

While that would be ideal, at least rinsing off before you get into your hot tub goes a long way to keeping contaminants out of the water.

And the dead skin cells? Those are constantly being shed, before, during, and after your shower, so there’s not really any way to rid yourself of them completely before you take a soak.

But taking a little extra time to exfoliate when you bathe can help remove more dead skin cells and send them down the drain instead of into your spa water.

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Shock Your Spa Regularly

Shocking your hot tub is part of your regular hot tub maintenance, which means you’re probably adding shock every two weeks or so.

But if you’re having trouble keeping the hot tub scum at bay, try shocking once a week instead. And remember to shock once a week anyway if your hot tub is getting heavy use, either with more people or more frequent use, or both.

Clean Your Hot Tub Regularly

After every soak, wipe down the headrests and any portion of the shell not in the water with a soft cloth or towel. Then at least once a week, use hot tub cleaner and a soft sponge to clean those areas and keep them free of contaminants. This will also help combat mildew.

Tip: To clean the water line without getting any cleaning chemicals in the water, use a dampened melamine sponge to wipe just above and below the water line.

Clean the Filter Regularly

Maintaining your filter will not only help keep the hot tub scum away, it’ll help your filters last longer, which will save you money in the long run.

Rinse your hot tub filter as often as possible with warm water or a garden hose and spray nozzle, especially if you’ve been using your spa more than usual.

Spray the filter once a week with a hot tub filter cleaner to gi e it a deeper clean. Don’t forget to rinse it afterward.

Soak the filter in chemical cleaner every time you drain and refill your hot tub to extend the filter’s life and loosen any stubborn particles. Rinse it thoroughly afterward.

When your filter gets to the point where even a chemical soak doesn’t completely clean it, it’s time to replace it

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How to Remove Hot Tub Scum

If all your preventive measures didn’t work, and a little scum was still able to form, you can remove it quickly and easily—most of the time.

Skim the Water’s Surface

Use a fine-mesh skimmer to scoop up any hot tub scum that’s collected on the surface of the water. If there’s a lot, rinse the skimmer between passes.

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Use Oil-Absorbing Sponges

You may have heard you can toss a couple of tennis balls into your hot tub to soak up oil, lotion, and other gunky stuff. This is true. In fact, we recommend it.

But while tennis balls will do in a pinch, they don’t have as much absorption power as the floating sponges made specifically for this task. Consider investing in a handful of these.

You can even have a couple of them floating around while you’re in the hot tub. They’re small and soft, so they won’t really get in the way. Plus, they come in cute shapes like turtles and stars.

Clean Your Hot Tub

Even if your spa water is balanced and doesn’t have a layer of scum floating on its surface, you can sometimes still see a ring of hot tub scum around the shell right at the water line. When this happens, it means whatever makeup, lotion, or other gunk floated along until it attached itself to the shell’s surface and started building up.

The good news is, it’s not in the water anymore. The bad news is … no wait, this is also good news! It means all you need to do is clean the water line.

Turn the hot tub off before you start. You may also want to remove some water from the hot tub to bring the water line below the scum line. You don’t want any cleaning products to get into the water because then you’ll be draining the entire tub.

Instead, scoop a few gallons out and set them aside in a large bucket. Then use hot tub cleaner and a soft cloth or a sponge, and gently scrub the scum line away. When it’s gone, pour the water back into the hot tub, and you’re back in business.

Remember to also clean the headrests and any other exposed parts of the shell to make sure no contaminants that may be lingering there find their way into the water.

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Clean or Replace the Filter

Even if you’ve skimmed the water, thrown in a few oil-absorbing sponges, and cleaned the hot tub scum line, you still have a scum problem—in your filter. Before you got that scum out of the water, it was passing through your filter. If you don’t also clean your filter when you clean everything else, you’re just inviting that scum back in.

In this case, though, just a rinse with plain water won’t be enough. You’ll definitely need to use a filter cleaner. You may even just want to skip straight to the chemical soak.

And if the cleaning doesn’t get the job done, just replace it. Filters are fairly inexpensive, and it’s better to start over with a fresh one than to perpetuate the scum problem by sticking a dirty filter back into your spa.

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Drain, Clean, and Refill the Spa

If you’ve done everything from skimming the water to replacing the filter, and you just can’t get rid of that last bit of scum that seems to be clinging to your hot tub for dear life, you’re left with one option: drain and clean your hot tub.

This is the last resort for addressing hot tub scum because, admittedly, it’s a hassle. It’s something you should be doing quarterly anyway, so having to tackle this big job in between regular drainings is irksome.

But if it’s between that and soaking in scummy water … well, you do the math.

Send That Scum Packin’!

No one should have to put up with any kind of scum in their lives, whether it’s hot tub scum or that terrible neighbor who sends their dog into your yard to do his business.

You may have a hard time keeping that dog in his own yard. But at least now when you stress about it, you’ll be able to relax in a nice, bubbly, scum-free hot tub.

Happy Soaking!

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Matt Giovanisci, Founder and CEO of Swim University
Matt Giovanisci is the founder of Swim University® and has been in the pool and spa industry since 1993. Since then, his mission is to make pool and hot tub care easy for everyone. And each year, he continues to help more people with water chemistry, cleaning, and troubleshooting.

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Save Time and Money with Our FREE Hot Tub Cheat Sheet
Download this FREE printable cheat sheet to keep your hot tub clean and clear. You’ll never worry about your hot tub again with this easy-to-use guide.