7 Warning Signs There’s Biofilm in Your Hot Tub

The longer biofilm is left untreated, the more of a risk it poses to your health. So what are the signs to look out for?

Telltale signs that biofilm is lurking in your hot tub are when the water is slimy, slippery, sticky, cloudy, or foamy; when the water smells like rotten eggs or plastic, when there is an increase in chlorine demand, and when the water turns pink.

Trying to fight biofilm by adding huge quantities of chlorine to your hot tub makes the water acidic. This has several adverse effects such as causing rashes and itchy skin and results in damage to your spa’s components.

Acting quickly is the key to preventing such issues. Here is an in-depth look at the 7 signs of biofilm.

1. Water feels slimy, slippery, or sticky

One of the major causes of slimy hot tub water is a build-up of bacteria and microorganisms that bind together to form biofilm. This bacteria can grow undetected in the pipes of your spa and can be seen on interior surfaces.

Biofilm can grow in a hot tub, skimmer basket, or even a filter. It likes areas that are warm and damp. The byproduct of biofilm is a greenish-white sticky residue that appears as a white film on your hot tub walls. This residue causes the water in your hot tub to feel slippery. 

If you’ve seen any unexplained green, brown, black, or white flakes in the water, chances are that your hot tub is infected with biofilm. If you notice a substance covering the water surface and/or near the jets and skimmer, that substance is most likely biofilm. It’s a bunch of bacteria secreting a protective layer of organic matter.

Biofilm is formed from the oil, grime, and bacteria that are introduced into your spa. Once your spa has biofilm, it can be difficult to maintain proper sanitation of the water. Biofilm makes the sanitizers in your hot tub less effective and causes the water to become more acidic. This can lead to health hazards and can also cause damage to your hot tub. 

2. Cloudy water

Another sign of biofilm in a hot tub is cloudy water. Biofilm can form rapidly in hot tubs that have been sitting empty or left open for a while. Water becomes cloudy when excessive biofilm builds up. It becomes white and milky.

Stagnant water is probably the main reason why biofilm grows. But if the climate is humid, biofilm can grow in the pipings even if the hot tub is empty.

3. Foamy water

One of the most common causes of foaming in hot tubs is a build-up of biofilm. Biofilm does not directly cause foamy water. However, it rapidly uses up the sanitizer (choline or bromine) residual in the hot tub water, which normally helps to break down the surfactants that cause foamy water.

With no sanitizer in the spa water, these substances build up much faster than normal and can rapidly lead to a foaming issue.

To get rid of foaming, you need to use a foam remover. Choosing a product from a trusted source is a good idea, but it’s important to remember that a foam remover does not cure the problem. 

To completely eliminate the biofilm from the hot tub, the pipes need flushing with Ahh-Some, and the water needs to be drained.

4. Water smells like rotten eggs

If your spa water smells like rotten eggs, there’s a high chance biofilm is present in the hot tub. The smell of rotten eggs in your spa is most likely caused by hydrogen sulfide gas. Hydrogen sulfide gas is not harmful, but the smell can be quite noxious. It is caused by decaying organic matter or by biofilm.

Organic matter can come from various sources. For instance, when you get into the hot tub, you introduce all sorts of organic matter, such as oils and dead skin cells. In addition, when you leave your spa cover off for a while, bugs and plant life can enter the hot tub.

Biofilm may be present in the hot tub water, but it’s more likely present in the hot tub plumbing and equipment. So, you want to ensure the dead animal smell is coming from your spa and not from your drains.

5. Water smells like plastic

The primary cause of a plastic smell in your spa is when biofilm is present inside the plumbing. This biofilm usually forms when the manufacturer is testing the hot tub system to ensure there are no leaks.

During the testing process, a small amount of water gets passed through the plumbing system. The water stays there for a long period before the hot tub gets used by a customer or is treated using chlorine. It is this water that causes the build-up of biofilm in the hot tub.

6. Increased chlorine demand (level keeps dropping)

Another sign of biofilm in a hot tub is increased chlorine demand. Chlorine demand is the amount of chlorine used up by reacting with substances in the hot tub water. One major cause of chlorine demand is contaminated water. 

Your water may contain contaminants like bacteria, fungi, and algae. As the chlorine reacts with these contaminants in the water, some of the chlorine is used up. This usually leads to the formation of biofilm on the surface of your hot tub. 

Biofilm forms when bacteria or microorganisms stick to a surface in contact with water. Biofilm is resistant to chlorine and will cause the chlorine to disappear from the hot tub water. This is because the chlorine is continuously working to eliminate the biofilm.

7. Pink water

The pink slime in your hot tub water isn’t a type of algae. Rather, it is a biofilm formed by colonies of the bacterium Serratia marcescens. The bacteria is closely related to white water mold and is very common. It is often found in bathrooms where it displays as pink rings and streaks.

Hot tub water turning pink isn’t very common in spas and only happens in very mature colonies. Serratia marcescens can grow in hot tubs because it’s highly resistant to chlorine, bromine, and mineral sanitizers.

This type of bacteria thrives in dark and damp conditions, and its growth is accelerated where there are phosphorus or fatty residues such as soap or shampoo. It is also introduced to hot tubs by the wind and rain because it is airborne. 

Serratia marcescens is usually nothing to worry about; however, it can cause problems for people whose immune system is severely compromised. If you wear a respirator, catheter, or any other medical device, you should avoid bathing because the device can provide a means for the bacteria to enter your body.

How to remove biofilm

Below is a list of materials and a step-by-step guide to removing biofilm from a hot tub. If you would like more information, check out my complete guide to getting rid of biofilm.

Tools needed

Step-by-step guide

1. Remove filters and clean them thoroughly. If you’re unable to clean the filters thoroughly, you will have to replace them.

2. Add Ahh-SomeOpens in a new tab. plumbing cleaner (also known as line flush) to remove the biofilm from the plumbing. Allow the cleaner to circulate for at least an hour. But if the hot tub hasn’t been used in a long time, let the flush circulate for several hours or, even better, overnight.

3. After cleaning/replacing the filters and adding a line flush to the hot tub, drain the water.

4. After draining the hot tub, clean the hot tub shell using a hot tub surface cleaner. Allow the cleaner to work for 15 minutes, then use a soft microfiber cloth or non-scratch sponge scrubber to remove the chemical residue.

5. Rinse the hot tub shell thoroughly. 

6. Ensure that all the jets are open once you’ve finished cleaning to reduce the risk of water pressure problems caused by trapped air.

7. Next, drain the rinse water from the spa by connecting the hose to the hot tub drain.

8. After draining, there’ll be an inch or two of water sitting in the footwells. You can remove it using either a wet/dry vac (faster and easier) or soft microfiber cloths to soak up the remaining water.

9. Once the hot tub is completely dry and sparkling clean, you can go ahead and refill it. Before refilling, ensure the breaker switch is off, and the hot tub drain is closed.

Joshua Milton

Joshua Milton is a seasoned hot tub enthusiast. With many years of experience in the industry, he offers valuable insights on hot tub maintenance, health benefits, and relaxation techniques.

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