Hot Tub Scum – How to Remove and Prevent It Like a Pro

Michael Keenan


Hot Tub Troubleshooting

Have you ever noticed an unpleasant layer or lining of an oily substance on the surface of your hot tub? That’s hot tub scum right there! It can occur due to poor quality, poor maintenance or too many contaminants in the water.

If left untreated, hot tub scum can lead to skin infections, rashes, red eyes and ear infections. So, not great.

This guide covers the different types of hot tub scum that form due to different causes such as water chemistry imbalance and inadequate sanitizer use. Then I’ll explain how to remove hot tub scum and show you ways to prevent scum being a problem again.

Let’s get into it now.

hot tub water with scum problem

Quick Answer:

Hot tub scum is an oily, sticky layer or lining in your hot tub caused by poor water chemistry, improper maintenance, inadequate sanitizer use, filtration problems, high usage rates and more.

To get rid of it you should use a skimmer net to scoop out the scum, clean the filters and surfaces with vinegar and baking soda and replace the water. To prevent it, take a quick shower before entering the tub and maintain pH levels while using shock treatments regularly.

What Is Hot Tub Scum Exactly?

Hot tub scum refers to a layer or lining of an oily and sticky substance in your hot tub. It might either float around on one part of the water’s surface or might be stuck on the surfaces of the walls of the tub. It can also form rings on the walls.

This usually looks highly unpleasant in the tub and may also lead to various issues if it comes in contact with your body.

There are times when this scum combines with the foam in your tub due to too many contaminants and plenty of aeration.

The Potential Health Risks of Hot Tub Scum

The scum present in your hot tub can lead to various health risks, some of which include:

  • Skin infections
  • Rashes and itchiness
  • Red eyes
  • Ear infections
  • Diarrhea/vomiting
  • Chronic infections

The bacteria present in this scum can enter your body and result in a variety of changes and illnesses. If you notice some of the above signs, make it a point to see the doctor for some medication or treatment advice.

arms with a skin rash

Common Types of Scum

The scum in the hot tub can take various forms based on what caused it. This can then determine the color of the scum too, with the three main types of scum being the following.

  • White Scum: White scum in the hot tub is likely to be a result of excess calcium levels in the water. This may result in the mineral gathering and forming a layer of white scum or even a white ring on the surface.
  • Brown Scum: If you notice a brown oily substance in your hot tub, this is most likely to be a result of an imbalanced water pH level. Typically, when the pH becomes too alkaline or basic, the minerals present in the water end up reacting with each other, including chlorine.
  • Green Scum: Metals and contaminants in the hot tub water may result in green scum forming a ring or layer. Excess levels of minerals like copper and magnesium may also result in this kind of scum.

Don’t get confused with hot tub foam – I have a guide on the causes of hot tub foam and then how to remove hot tub foam – check them out!

Causes of Hot Tub Scum

Given that hot tub scum is of different types, it is also possible for the causes to differ. A combination of factors can also help explain the formation of the scum. Take a look at some of these main causes of hot tub and spa scum:

  • Poor Water Chemistry: The pH levels can sometimes become too high in the hot tub or the water might be too hard (calcium hardenss). This can alter the required balance in the water, resulting in scum building up.
  • Poor Maintenance and Cleaning: If you don’t clean the water nearly every week or leave the tub unused and uncovered, this can become a sure way for the scum to develop.
  • Inadequate Sanitizer Use: Chlorine or bromine sanitizers are necessary to add to the hot tub once or twice a week to clean the contaminants. Leaving long gaps between each sanitizing moment can allow the contaminants to fester.
  • Filtration Problems: Your hot tub’s filter might be too dirty or even clogged, preventing it from filtering out the gunk properly.
  • Age and Degradation of Components: Old hot tubs are more likely to see scum due to the components wearing out and interacting with the water and minerals. The formation of rust can lead to scum too.
  • High Levels of Organic Matter: Algae, leaves, oils, hair, dead cells, and more can gather in the water and lead to the formation of scum.
  • High Usage Rates: If you use the hot tub multiple times every week or if too many people use it at once, many products and waste may collect in the tub.

Find out how I get rid of white mold in my hot tub here! Some useful tips.

How to Remove Hot Tub Scum

There are some simple solutions to help you get rid of the scum in your hot tub. Read through them below.

Use Skimmer Net

If it’s not too bad yet or maybe you notice a few clumps floating on the surface, you could just skim it off. Take a mesh skimmer net made from nylon or polyester and scoop all the scum out by coursing it through the water in the hot tub. Use the handle to adjust the coverage.

Use a Sponge

Special sponges made for hot tubs or swimming pools can soak all the oils and contaminants to clean the water. These can be quite effective believe it or not! Simply place the sponge in the hot tub and leave it for a few hours or even better, overnight. Then remove the sponge – hopefully it has soaked up most of the scum!

Clean the Biofilm

Biofilm forming due to mold or slime may sometimes result in scum too. Buy a biofilm cleaner to break it down to get rid of the scum.

Clean the Surfaces

Once you manually remove the scum, drain some or all the water and work on the spots that had the scum rings. Use vinegar or baking soda for this and rinse it out carefully.

If you have a “tide line” around the hot tub you might not need to drain your tub completely. Just lower the water level to be able to clean the ring. Remember to test the water after refilling and balance your chemicals again.

The above tips are good if your hot tub scum problem is not too severe. If it is really bad or is happening again and again, it’s best to completely clean your hot tub and start from scratch.

cleaning a spa with gloves and a sponge

Getting Rid of Severe Hot Tub Scum

Sometimes you just need to do the job right! Follow these steps to remove that scum completely:

  • Drain and clean your hot tub completely – follow my guide here. Make sure you do it right!
  • Clean or replace the filter – If the filter is in good enough order give it a good clean or better still soak it overnight in a filter cleaner solution. (10% bleach/water mix works well). Rinse well before replacing.
  • Flush the lines – flushing all the pipework will remove all traces of impurities such as biofilm. You don’t want any old gunk in the pipes flowing back into your freshly cleaned hot tub!
  • Refill your hot tub – top tip, use a hose filter when refilling to make sure no impurities are added from your water source (or dirty hosepipe).
  • Add your chemicals – make sure to heat your spa before adding your chemicals again. Then proceed to balance the water.
  • Test your hot tub water – as always test again before using the tub. Safety first!

It is a bit of work but you should be refilling your hot tub around every 3 to 4 months anyway. If you have scum it’s worth doing it a little early.

Ways to Prevent Hot Tub Scum Forming

Getting rid of the scum is one thing, but you must also make an effort to ensure that the scum doesn’t return to the water in your hot tub. Here are some ways to prevent scum formation.

Shower First

Always make it a point to take a quick shower or rinse before you enter the hot tub. This will remove all the dirt, oils, lotions, and soaps from your body.

Maintain pH Level

You must always keep the pH level balanced, with a good range being 7.2-7.8. Add pH reducers or increasers so that you can correct the pH whenever needed.

Use Shock Treatment

Shock treatments allow the sanitizer to work properly while also breaking down the contaminants. Shock your hot tub once a week (more or less) depending on how often you use the tub.

Use a Clean Filter

Your hot tub’s filter should always be clean and clear to ensure good filtration. Clean it monthly to keep it functioning properly and make replacements if it wears out.

Keep Testing the Water

You must keep testing the water in your hot tub regularly – at least weekly. This will help you keep track of the pH levels and other standards.

Keep Surfaces Clean

Inspect your surfaces often to spot dirt, organic matter, or grease. Even if you do not spot them, you must wipe them down after every few uses. Perform a deep clean 3-4 times a year whenever you replace the water.

outdoor shower

Key Takeaways

Don’t let hot tub scum become a problem. If you follow my advice above it’s easy to prevent scum forming in the first place. A few simple measure and a good maintenance schedule will be enough in most cases.

When you do spot scum forming in your spa, act quickly. If in doubt, just go the whole hogg and drain, clean and refill your hot tub.

There you have it!

michael keenan author

Author - Michael Keenan

I'm Michael Keenan the owner and creator of the Outdoor Care Guide. I'm a trained horticulturist with over 30 years of experience in pool care, plant care, and landscape care! Seemed like a good idea to share - I think I can make your life easier and save you some time and money!