Hot Tub Scum (How to Get Rid and Prevent The Scum)

Scum is a type of mineral buildup that forms on the water’s surface. It develops due to an imbalance in chemical compounds, namely calcium and magnesium.

You can remove the scum in the hot tub using an acid wash with hot water, white vinegar, hot tub shock, or filter cleaner for the hot tub filter.

This prevention article will outline how you can get rid of hot tub scum before it becomes a problem that requires professional help.

What Causes Hot Tub Scum?

It is important to note that hot tub scum is not the same as a hot tub stain.

Hot tub stains result from chemical compounds and metal elements in your water reacting with certain chemicals and minerals that naturally occur in tap water.

These reactions create different pigments which end up coloring your hot tub surfaces (i.e., vinyl, fiberglass, marble, tile).

Hot tub scum is another issue.

The scum in your hot tub is actually calcium carbonate.

This mineral compound builds upon hot tub surfaces over time due to the presence of calcium and magnesium in the water.

It appears as a film or layer on the surface of the water. It can appear cloudy, white, or even brown in color.

Hot tub scum because of bad bathing habits

Some of the biggest reasons for scum forming in your hot tub are body care products, bodily residue, and even metals.

  • Body Care Products: Body care products like soaps, lotions, oils, and perfumes will leave a residue when they are added to hot tub water. A chemical film called “biofilm” is created in your hot tub whenever someone uses it.
  • Bodily Residue: Bodily fluids like sweat and urine contain urea, which will react with chlorine. As a result of this reaction, scum is created and will appear on the surface of your hot tub water.
  • Metals: Metals such as iron and copper in tap water can affect certain chemicals’ ability to do their job. Keep an eye out for metals in your hot tub and have regular tests done on your water.

So what can you do to prevent scum from building up in your hot tub?

First, try not to use body care products when using the hot tub.

If you must use them, rinse all of them off before getting into the water.

Hot tub scum because of poor water balance

But in most cases, poor water chemistry and a worn-out filter are the main reasons for scum formation.

Regular hot tub maintenance is essential!

A common misconception about hot tubs and hot tub maintenance is that a chemical imbalance will just sort itself out on its own over time, without any intervention needed from you.

But I have to tell you. This is not true!

It is your responsibility to keep the hot tub clean and maintain the water balance.

In case of a water chemistry problem arising, you have to take action before the problem becomes worse.

Water chemistry is all about balance – too much of something or too little of something can create an imbalance in your water, which leads to problems like scum formation.

And if left untreated for too long, scum will accumulate, and a hot tub leak may even become a real problem.

But to prevent all that, you need to take action before this happens!

Hot Tub Scum Types

You should know that there are two types of hot tub scum. The first type is surface scum which coats the water’s surface. It can be easily removed with agitation (i.e., brushing, wiping), but it will continue to reappear until you address the cause.

The second type of hot tub scum is the bottom scum.

This is the most challenging type to remove because it is not as easy as simply wiping or brushing away.

Bottom scum does not come off with agitation and will require a professional hot tub cleaning with powerful chemicals and brushes to forcibly remove this particular mineral compound from your hot tub surface.

  • Brown Scum: Calcium, iron, and manganese react with chemicals in the water to create certain pigments, which can cause a brown color.
  • Green Scum: Verdigris is a natural or artificial patina that forms when the copper reacts with air or water. In a hot tub, certain compounds can cause a green coloration to develop on the surface of your hot tub.
  • Blue Scum: Copper reacts with either air or water to create a blue-green color found in hot tub scums.

Hot tub scum is not only unsightly, but it can cause health problems if you breathe in the mineral deposits.

Additionally, hot tub scums can clog up drains and filters, making maintaining your hot tub more difficult and costly.

How to remove the scum in the hot tub?

There are many solutions to the problem with scum in the hot tub.

Here is a list of the most common methods to get rid of the scum in a hot tub:

  • Using an acid wash with hot water.
  • Use white vinegar in the hot tub.
  • Use filter cleaner for your hot tub filter.
  • Use special chemicals designed to clean mineral deposits from hot tubs.

Remove scum in the hot tub with an acid wash

First, you will have to use a pH test kit to determine how acidic your hot tub’s water is.

This is important, as the solution must be more acidic than the hot tub water.

If there is no test kit, you can tell by performing a simple litmus paper test – put the end of a strip into your hot tub.

If it turns pink, it’s alkaline; if it turns blue-ish green, then the pH is within.

  1. If the scum in your hot tub is not too bad, you can simply use an acid wash with hot water to remove it. Prepare a mixture of 2 gallons of water and 1 cup of muriatic acid.
  2. Pour the mixture into your hot tub, then let it sit for at least an hour. After this time, run fresh water through the hot tub to remove any scum that remains.
  3. Rinse well with plain water before using your hot tub again.

Remove scum with white vinegar in the hot tub

Using white vinegar is another method you can try to get rid of the scum in your hot tub.

  1. First, pour 1 cup of white vinegar into your hot tub water and let it sit for an hour.
  2. After the time has passed, turn on your jets and run fresh, clean hot tub water through them to get rid of any remaining scum.
  3. As with the previous method, rinse well with just hot water before using it again.

Use filter cleaner for your hot tub filter

Filter cleaner is designed to remove calcium and magnesium deposits without harming your hot tub’s equipment.

It is available at most pool stores.

You will have to use it per the manufacturer’s instructions.

Use special chemicals designed to clean mineral deposits from hot tubs

Chemicals are the most effective way to get rid of hot tub scum. Most chemicals can be used in either a powder or liquid form.

You will need to follow the manufacturer’s instructions precisely, as these chemicals are very potent and must never come into contact with your skin.

After using any of these methods, you should use a pH test kit to ensure the hot tub water is at an appropriate level.

Then, you can enjoy your clean, crystal clear hot tub.

What is that white scum ring around the hot tub?

Maybe you’ve even noticed it. There is a white scum ring around the hot tub, and you might be wondering what’s up with that.

First of all, don’t panic!

This is actually quite normal. The white scum ring you see in your hot tub is calcium buildup – water full of calcium, magnesium, and other minerals.

A buildup happens when the chemicals in your hot tub are not balanced.

  1. First, you have to determine the pH and alkalinity of your hot tub. Proper chemical balance is necessary for clean water in any hot tub.
  2. Pour some acid into the hot tub and lower pH below 7.0 – this is important.
  3. Let the filter run for a few hours to see if it clears up.
  4. Then brush the white ring away. Be sure you use all necessary safety precautions when handling chemicals.
  5. If necessary, repeat this process until the water is clear.
  6. Finally, follow the manufacturer’s instructions for re-balancing your hot tub water.

What you need to know now is how to prevent the white ring in your hot tub.

  • Use a stronger filter pad – these work well for hot tubs with a lot of calcium buildup.
  • Put a hot tub cover on the hot tub when it’s not in use.
  • Use a clarifier to help break down hard water and get rid of the scum.

You should also test your hot tub regularly for pH levels and preventative chemicals to avoid any calcium or other minerals problems.

How to get rid of film on hot tub water

You may notice a film on your hot tub water or a white ring around the edge of the hot tub.

This is caused by body oils, sweat, bathers’ lotions or creams, and other chemicals that are left behind on the hot tub itself.

I know, hot tubbing can get a bit messy!

Fortunately, cleaning the hot tub and getting rid of this film is relatively simple:

  1. First, you need to test your hot tub water for pH levels – too low or too high a level will cause problems with scum.
  2. After adjusting, add a few drops of chlorine bleach to the hot tub. Be sure to turn off the hot tub’s filter pump before using these solutions.
  3. Then start up your filter and let it run for a few hours.
  4. If the hot tub water film is still there, shock your hot tub again!

Your hot tub should be clear after this!

Be sure to check again that it’s at an appropriate pH level as well as re-balance as indicated by the manufacturer of your hot tub water system.

How to prevent scum from forming in the hot tub?

The best way to prevent scum in your hot tub is to use a good balance of excess calcium and magnesium.

Another solution is to use an acid wash every six months.

However, none of these solutions are as effective as taking necessary precautions when filling the hot tub with water.

Ensure that your hot tub’s filtration system uses either hot tub sand filters or cartridge filters. Many hot tubs use an ion-exchange system, which does not work well with acid washes to remove scum.

While filling the hot tub with water, turn on the filter. This will start removing any loose particles that have already accumulated in the hot tub.

Fill it gradually, as recommended by the manufacturer of your hot tub. If you fill it too quickly, you run the risk of the scum being churned up and recirculated.

Other tips:

  • After draining the hot tub, make sure you clean it thoroughly. You can wipe down the exterior with a pH-balanced cleaning solution designed to remove scum.
  • Letting your hot tub settle before using it allows water-soluble particles of calcium and magnesium to precipitate out of suspension.
  • Clean your filter weekly. Using filter cleaner every 12 months will also help keep your hot tub running smoothly and keep it free from scum.
  • Pour out the water from your hot tub if not used for a while (especially during cold winter months).

Do you have any further questions about hot tub scum?

Contact me at @contactswimfool on Twitter, Facebook, YouTube, or Pinterest – I’ll be happy to help.

Have fun in your clean hot tub!

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Hi. I'm Max Berg. I've been in the pool industry since 2015 and have always felt drawn to water. I'm the author behind swimfool.com, where I share my years of experience in pool maintenance and give helpful tips on keeping a swimming pool or hot tub clean. My tips reduce the costs of water treatment and protect the environment.

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