How to Remove & Prevent Hot Tub Scum (Brown, Green, Blue-Green)


I know how disconcerting it can be to peel back your spa cover to reveal a disgusting-looking scum floating on the top of the water. But the good news is that you don’t need to worry. It’s really easy to deal with.

Hot tub scum is caused by bodily secretions, personal care products, high levels of metals, water chemistry imbalance, and dirty or worn-out filters. There are three types of spa scum, so you must identify which type has formed in order to treat and remove it. Preventative measures can be taken to avoid scum from reoccurring.

In this article, I show you:

  • What caused the scum in your spa
  • How to identify which type has formed
  • How to get rid of the scum
  • How to ensure it doesn’t come back in the future

The 5 causes of hot tub scum

Take time to read through carefully as the scum in your spa may have been caused by a variety of factors.

Bodily secretions

Your body sweats as many as three pints (1.7L) for every hour you sit in a hot tub at 102°F (39°C). As the natural fluids and residue wash off our bodies, they introduce around 100 million new bacteria to the spa water.

Our bodies lose as many as 40,000 dead skin cells every minute, and this process is only accelerated by sitting in warm, bubbling spa water.

Adding to the 100 hairs we lose each and every day is our bodies’ sebaceous gland that opens into the hair follicles to secrete an oily or waxy matter known as sebum. Where does that sebum end up? In the hot tub soupOpens in a new tab..

And let’s not forget all the other natural bodily fluids such as blood, saliva, mucous, urine, and fecal matter. If these are not dealt with properly, they cause a nasty-looking scum to appear.

Personal care products

In addition to the natural bodily fluids we introduce are the man-made products that keep our bodies and swimwear clean, hygienic, and smelling great.

These include deodorant, soap, shampoo, gel, hairspray, fragrances, lotions, cosmetics, laundry detergent. The list goes on and on.

All these products play havoc with the water chemistry in your spa, causing scum and other clarity problems.

High levels of metals

All water sources contain at least some levels of natural metals, such as copper, iron, and magnesium.

Depending on where you live in the world, these levels can be extremely high. In fact, one of the hardest sources of water is from private groundwater wells, which some 15 percent of Americans rely on daily.

Not only do these metals react with chlorine to oxidize and stain your hot tub shell, but they may also cause a green-colored scum to form on the water’s surface.

Water chemistry imbalance

If you allow your spa water to become unbalanced and, in particular, allow the pH levels to become too high, you’re creating the perfect environment for algae and other bacteria to thrive, which can result in hot tub scum.

Unsanitary water can make you very sick, exposing you to viruses and diseases such as hot tub lung, hot tub rash, E. Coli, Legionnaires’ disease, and urinary tract infection.

Problems with filtration

It’s important to think of the filter in your spa as your hot tub’s kidneys. Just like the kidneys in your own body, the filter keeps the water clean by removing as much unwanted material as possible.

But if you don’t keep on top of the weekly maintenance schedule required to keep the filter working properly, it’ll soon become too dirty and clogged to filter out all those scum-causing contaminants that you and your family introduce with every use.

Even if you don’t use your spa all that often, your filter has a limited lifespan and should be replaced after one year. If your hot tub is used on a regular basis or gets used by a lot of people, then replace the filter more often.

Types of hot tub scum

Now you know the reasons why hot tub scum occurs, it’s time for you to identify which type has formed in your hot tub. How can you do this? By color.

Brown scum

A brown ring running around the water line or a brown layer that floats on top of the water indicates a high pH level.

High pH causes minerals such as iron to react with the sanitizing chlorine, resulting in the brown scum you see on the surface of the water and on the sides of the spa shell.

Green scum

Green scum indicates that there is too much copper or magnesium reacting with the chemicals in the water.

This is the same reaction you see from an old copper penny or roofing made from copper: it forms a greenish tint.

Note: Sometimes, the water may have a greenish tint shortly after using hot tub shock as the oxidization reacts with the copper minerals in the water. If this happens, treat the water with spa metal removerOpens in a new tab..

Blue-green scum

A blue-green (cyan) scum is the worst type. It’s caused by a combination of high levels of metals, bodily fluids, and personal care products that aren’t being properly dealt with by the filter.

You must be very careful if blue-green scum has formed in your hot tub as it poses the highest risk to the user.

Blue-green scum is the most difficult type to remove; however, the good news is that once it’s gone, preventative measures should stop it from returning.

How to get rid of hot tub scum

The first thing you must do to get rid of hot tub scum is to use a fine-mesh skimmerOpens in a new tab. to skim off the majority of the scum that’s floating on the surface. If you have a real lot, rinse the skimmer each time between passes.

As with any water clarity issue, it’s a good idea to give the filter a thorough clean using a chemical soak. More information on filter cleaning under the section on removing blue-green scum.

How to remove brown scum

Since brown scum is caused by high pH, you’ll need to use pH decreaser. The optimum pH levels for hot tubs are between 7.4 – 7.6.

You may read elsewhere that a range of 7.2 – 7.8 is acceptable. While this is true, keeping it within the optimal range gives you breathing room should things change unexpectedly.

Having said that, if brown scum reappears more than once after using pH decreaser, try keeping the pH level between 7.2 – 7.4 for several months to see if that resolves the issue.

How to remove green scum

Because green scum is caused by high levels of metals, you’ll need to add metal sequestrant to the spa water. Rather than remove metals from the water, metal sequestrant clumps them together so that they’re large enough to be removed by the hot tub filter.

If the water where you live has high calcium levels, then it’s better to use this particular spa stain and controlOpens in a new tab., which is a special type of metal sequestrant that also deals with excess calcium.

Up to 98 percent of the impurities in the water can be removed simply by attaching an inexpensive inline pre-filter to your hose.

This simple piece of kit will go a long way to preventing green scum from forming on subsequent fills, and it means that you’ll be starting with cleaner and fresher water that doesn’t need so many chemicals to keep it balanced.

How to remove blue-green scum

Blue-green scum is caused by a combination of factors, so tackling the issue requires the use of chemicals alongside preventative measures.

The first thing to sort is your dirty or worn-out spa filter. It needs to be removed from the filter well, gently hosed down, and placed in a chemical soak for 24 hours.

Once complete, remove the filter from the soak and rinse with fresh, clean water. It’s a good idea to use a filter comb between the pleats to ensure all traces of dirt are removed.

If you can’t get the filter clean after a chemical soak, or the filter is more than 12 months old, then it’s time to replace it. For more information, check out my guide to filter maintenance.

With the filter sorted, you’ll now need to address the issue of excess metals. This is done in the exact same way as you would with green scum.

To stop blue-green scum from returning, you’ll need to implement a regular cleaning routine alongside some preventative measures to stop impurities from entering the water unnecessarily.

7 ways to prevent hot tub scum

Trust me, I get how much of a drag maintaining a hot tub can be. But being proactive when it comes to maintenance can save you time and money in the long run. Prevention rather than cure.

Perform regular water tests

The only way to control the water chemistry is by performing regular tests. Test strips and liquid test kits will enable you to keep on top of the pH levels, which is vital to prevent the scum from reoccurring.

Depending on where you live, you may also need to purchase special metal test stripsOpens in a new tab. if you suspect that the water in your area contains high levels of metals.

High mineral levels are a common problem for people living in cities and for those that source their water from groundwater wells.

You need to be testing the water at least once per week. But if you’re experiencing issues with hot tub scum, water clarity issues, or the hot tub is being used a lot, it’s important to test the water more often.

Shower before getting in your hot tub

A large number of bodily secretions and most personal care products can be removed simply by washing with soap in the shower before getting in the hot tub.

If that seems like a lot of hassle, then at least jump in and rinse off first. You could even rinse off using the garden hose.

While there’s nothing you can do to completely prevent dead skin cells from entering the water, you can take the time to exfoliate with an exfoliating cloth to reduce that number.

Use floating sponges

You might have heard of spa owners throwing a couple of tennis balls into their hot tub to soak up stuff in the water that shouldn’t be there.

While this is better than nothing, it’s better to use specially designed floating sponges for more absorption power.

These synthetic sponges are made from polyurethane, which attracts oils, lotions, and other gunk that we introduce from our bodies and swimwear. Just toss a couple into the water and let them do their thing.

Keep the filter clean

I know it’s a pain, but you must keep your spa filter looking like new to avoid issues such as hot tub scum. This is what your filter maintenance routine should look like:

Weekly: Rinse the filter thoroughly with fresh water from your garden hose.

Monthly: Spray the filter all over with filter cleaner and allow it to sit for 15 minutes. Rinse off and allow to air dry.

Quarterly: Place the filter in a chemical soak for 24 hours to remove all traces of dirt and grime. Rinse thoroughly and allow to air dry before replacing. If this doesn’t get the filter clean, replace it immediately.

Yearly: No matter how little your spa has been used, replace the filter with a new one.

For weekly cleans, you may use a vinegar-water solution to clean the filter. Ensure that you rinse thoroughly afterward if you do decide to use vinegar as it can cause problems with water clarity.

Never use a power washer or bleach as it damages the filter’s fibers.

Keep your hot tub clean

It’s important to keep the hot tub shell and headrests clean after each use, which can be done using a soft cloth.

Once a week, use this hot tub surface cleaner with a soft sponge to clean and kill bacteria in areas above the waterline. Do not let any cleaner enter the water as it will cause an imbalance.

For cleaning along the waterline, you have two options:

  • Remove a portion of the water into a clean bucket and wipe along the waterline.
  • Use a melamine sponge (magic eraser) to clean along the waterline. This avoids the risk of introducing chemicals into the water.

Shock your hot tub regularly

It’s advised to shock a spa once every two weeks. But if you’re having trouble with scum forming, then try shocking on a weekly basis.

Chlorine-based shock can be used if your sanitizer is either chlorine or bromine. It’s much more effective at treating scum than non-chlorine shock.

It’s a good idea to shock your spa immediately after it’s had a lot of heavy use or has seen a high bather load.

Drain your hot tub every 3 months

Under most circumstances, it’s necessary to drain a hot tub every three to four months to prevent clarity issues like cloudy water, foam, and scum.

Each time you add chemicals to your spa, you add to the saturation levels. Water can only tolerate so many chemicals before they become ineffective at sanitizing.

Remember the chemistry experiment you performed in school where you added one tablespoon of salt at a time to a glass of water?

At first, the salt dissolved. But as the water reached its saturation point, the salt would fall and sit on the bottom of the glass as the water was no longer able to dissolve it.

This is the same thing that happens to your spa water as you constantly add chemicals over time.

Refilling your spa with fresh water resets everything so you can start from scratch. It also gives you chance to remove any harmful biofilm lurking in the plumbing and allows you to disinfect the empty hot tub shell.

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