How to Banish Hot Tub Scum & Prevent It From Coming Back

There's no worse feeling than opening the cover to reveal your hot tub has developed a scum line along the water's edge. Ew. If you've spotted some scum lurking in your tub, don't worry, we're here to help.

In this blog post, you'll learn what causes hot tub scum, how to prevent it from appearing in the first place, and how to remove it on the unfortunate occasion that it does appear. Keep reading for our scum-busting tips.

What Causes Hot Tub Scum?

There are several issues that can cause hot tub scum, including:

• Bodily residue: People’s skin naturally contains oils and sweat that can contribute to scum buildup when they get in the hot tub.
• Environmental debris: Leaves, dirt, pollen, and other environmental debris can also contribute to scum buildup by providing a surface for bacteria to adhere to.
• Chemical imbalance: An imbalance in your hot tub's chemicals can cause scum as well.
• Personal care products: Soaps, lotions, and other personal care products can also contribute to scum buildup in hot tubs.
• Metals: The water in your hot tub contains certain metals, like iron and copper, that can cause scum when they react with your sanitiser.
• A worn or unclean filter: A worn-out or dirty filter can allow scum-causing particles to remain in your water.

Different Types of Hot Tub Scum

There are three main types of hot tub scum that you will encounter:

1. Brown scum is usually caused by a pH level that is too high
2. Green scum is usually caused by high levels of copper
3. Blue-green scum is usually caused by a combination of factors, such as an unclean filter, personal care products and environmental debris

Each type of scum requires a slightly different approach. While 1 and 2 can be fixed by simply draining, cleaning and refilling the tub (or correcting a chemical imbalance), 3 will require a combination of techniques to restore equilibrium.

How to Treat Hot Tub Scum

The method you choose will depend on the type of scum you've identified:

Brown scum

The first thing to do is to test the water's pH. If it's too high, that's likely the cause of your scum problem. To correct it, you'll need to balance the pH level. This can be done by:

1. Gather your supplies: To test and correct the pH levels in your hot tub, you'll need a pH test kit or test strips, pH increaser (sodium carbonate), pH decreaser (sodium bisulfate), and a container for collecting water samples.
2. Turn on the hot tub: Activate the hot tub's circulation system to ensure that the water is well-mixed before testing.
3. Collect a water sample: Using a clean container, scoop out a sample of the water from the hot tub. Be sure to collect the sample away from any jets or return lines, and at elbow depth to get an accurate representation of the water's pH.
4. Test the pH level: Follow the instructions included with your pH test kit or test strips. This usually involves dipping the strip into the water sample or adding a reagent to the sample and comparing the colour change to a provided chart. The ideal pH range for a hot tub is between 7.4 and 7.6.
5. Determine if adjustments are needed: If the pH level is within the ideal range, no further action is required. If the pH is below 7.4, you'll need to raise it. If the pH is above 7.6, you'll need to lower it.
6. Adjust the pH level: To raise the pH, add a pH increaser (sodium carbonate) according to the manufacturer's instructions. To lower the pH, add a pH decreaser (sodium bisulfate) following the manufacturer's guidelines. Make sure to add these chemicals gradually and in small amounts to avoid overshooting the desired pH range.
7. Mix the chemicals: Turn on the jets and let the hot tub run for at least 30 minutes to ensure proper mixing of the chemicals.
8. Re-test the pH level: After the chemicals have had time to mix and circulate, collect another water sample and test the pH level again. If the pH is still outside the ideal range, repeat steps 6-8 until the desired pH range is achieved.
9. Monitor and maintain: Regularly test the pH levels in your hot tub, ideally once a week, to ensure they remain within the recommended range. Make adjustments as needed to maintain a balanced pH level, and enjoy a safe and comfortable hot tub experience.

Green scum

As green scum is usually caused by copper, the best way to deal with this issue is to drain, clean and refill your hot tub. We can recommend that you use a metal sequestrant (such as Sodium Thiosulfate) to increase the amount of copper filtered out of your water.

Blue-green scum

If you've noticed a blueish-green scum, the best course of action is to drain, clean and refill your hot tub. To do this, you should:

1. Gather supplies: Get a submersible pump/garden hose, bucket, sponge, soft cloth, hot tub cleaner/mild soap, hose with a water filter (if needed), and necessary chemicals.
2. Turn off power: Disconnect the hot tub, and turn off the heater and timers.
3. Drain hot tub: Attach a pump/hose to the drain valve and direct it to a proper drainage area. Open the valve and drain completely.
4. Clean interior: Remove debris, then apply hot tub cleaner/mild soap to a sponge/cloth and gently scrub the surfaces. Avoid abrasive materials.
5. Rinse: Use a hose to rinse the hot tub thoroughly, removing all soap residue.
6. Clean filters and cover: Clean filters as per the manufacturer's instructions, and wash the cover with mild soap and water.
7. Close drain valve: Ensure the valve is securely closed before refilling.
8. Refill hot tub: Fill with fresh water using a hose with a water filter (if needed) up to the appropriate level.
9. Reconnect power: Reconnect to the power source, turn on the heater and timers.
10. Balance water: Test and adjust pH, alkalinity, and sanitiser levels. Allow water to circulate for 24 hours before use.
11. Monitor and maintain: Perform regular testing, cleaning, and maintenance for optimal performance.

Other ways to remove scum

If the problem doesn't seem too bad, you can simply deal with the scum that has appeared rather than draining the whole tub. To do this, you can:

• Skim the water's surface using a pool skimmer net. This will help to remove any scum that is floating on the surface
• Use an oil-absorbing sponge
• Brush down the walls and jets with a soft-bristled brush to remove any adhered scum or buildup
• Add an enzyme-based cleaner. Enzyme cleaners, utilising biological techniques, break down organic residues like stains and odours in hot tubs

Preventing hot tub scum

Keeping scum at bay doesn't have to be a daily chore. In fact, by incorporating a few good habits into your hot tub routine you can prevent scum 95% of the time.

Regular testing

You should test and adjust your hot tub's pH, alkalinity, calcium hardness and sanitiser levels at least once a week. This will ensure that the water is properly balanced and reduce the likelihood of scum forming.

Cleaning the filter

A clogged or dirty filter can prevent proper circulation in your hot tub, leading to scum buildup. Clean it regularly (at least once a month) to keep the water clean and clear.

Showering

Having a shower or bath before getting in the hot tub will help reduce the amount of oils, fragrances and personal care products that can contribute to scum formation.

Draining & refilling

This will allow you to remove any buildup of dirt, oils and debris that can lead to scum. Plus, it's an excellent opportunity to check for any signs of wear and tear that may need addressing.

Shocking your hot tub

Shocking your hot tub regularly (every 1-3 weeks, depending on usage) will help keep the water clean and clear and reduce the risk of scum forming. It's always best to test before you shock as too much of any one chemical can be as bad for your hot tub as too little.

We hope we've provided you with the battle plan you need to defeat scum once after all. If you're finding the whole thing a bit daunting, we recommend you review your maintenance routine (or create one if you don't have a routine) as most hot tub issues can be prevented well before they occur with regular testing and cleaning.

Happy hot tubbing!