What Does Biofilm Look Like In My Hot Tub?

What does biofilm look like in my hot tub

Imagine coming home after a long day daydreaming about taking a relaxing dip in your hot tub. You reach home and get ready, but as soon as you’re about to step into the tub a foul smell hits your nose. This bad odor is highly likely caused by biofilm formation in your hot tub you were not aware of.

But how can you be aware of something that you can’t even identify? Since biofilm formations don’t originate in the hot tub itself, a lot of hot tub owners don’t even know what it looks like. Here you’ll learn not only what biofilm looks like but a comprehensive rundown of the causes, treatment methods, and prevention methods as well.

Key Takeaways

  • Biofilm formations occur in the pipe systems, which is why it’s difficult to identify.
  • Biofilm formations can also occur due to the presence of excessive dirt, oil, and bacteria in the tub water that gets dispersed from human skin.
  • They’re highly resistant to usual hot tub water treatments, calling for specialized treatment for removal.

What Causes Biofilm Formations?

What causes biofilm formations
What causes biofilm formations

Biofilms are slime-like formations that occur as a super combination of bacteria, dirt, and other microorganisms present in a hot tub’s pipe systems. What separates biofilms from algae, stains, and other common hot tub contaminations is the fact that the slime-like layer it has is a protective one.

This layer is responsible for protecting the biofilm mass from the most common chemical treatments for bacteria and microorganisms. Once a biofilm formation occurs, the only way to rectify the problem is with a thorough cleaning of not only the tub but the associated piping system as well.

Biofilms thrive in warm, damp environments, so hot tubs make the perfect breeding ground for them. The worst part is, that future biofilm contaminations can be lurking in the brand-new piping system you’ve installed for your hot tub. If left untreated, biofilm contaminations not only become health hazards but also clog different hot tub components like the plumbing and filtering systems.

What Does Biofilm Look Like in a Hot Tub?

If the biofilm contamination is in its early stages, you can generally observe it at the bottom of the hot tub as well as the inner surface of a pipe. Beneath the slime-like protective cover, biofilms can be any color starting from moldy green to gooey orange depending on what bacteria and microorganism formations have developed it.

You’ll probably first notice biofilm formations due to your hot tub water becoming cloudy and giving off a foul odor, which is in the early stages of the contamination. At later stages, they can plop up as floating debris when they’ve grown large enough. Fully grown biofilm debris looks like chunks of liquid amber of various shapes and sizes.

Biofilm formations are pretty disgusting to look at and unsafe to touch. So if you notice them floating on your hot tub water after running it for the first time after a few months, you immediately need to take steps to decontaminate the pool.

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How to Treat Biofilm Formations?

How to treat biofilm formations
How to treat biofilm formations

Unlike other hot tub treatment methods, removing biofilm formations requires a thorough approach since the slime layer protects it from anti-bacterial solutions like chlorine and bromine. Here’s a step-by-step approach to treating biofilm formations in your hot tub:

  1. Apply Tube Cleaner: Tube cleaners are special cleansing products for piping and plumbing systems. Since biofilm formations primarily occur in the pipes, it makes sense you clean the plumbing system first by purging it with the tube cleaner so the biofilms flow through the pipes and end up in the hot tub to make the cleaning process easier.
  2. Removing and Sanitizing the Tub Filter: Biofilms often tend to clog your hot tub’s filters first so that they have more bacteria and microorganisms to assimilate with. So your second step should be to detach the filter, clean it properly, and then sanitize it by submerging it in chlorinated water for at least 3 days.
  3. Super Chlorinate the Tub: Though it might sound fancy, the principle behind this process is simple- add large amounts of chlorine to the hot tub (granular chlorine is preferable) and keep the water running for 72 hours. Running chlorinated water for this long will ensure that it reaches the deepest part of your plumbing system and loosens the toughest biofilm formations from the pipes that haven’t come loose yet.
  4. Draining the Tub: Once the tub has been super chlorinated, drain the tub completely releasing all the jets and valves. All the biofilm formations should flow through the tub’s drainage at this point, leaving the tub clean of any traces of biofilm.
  5. Refill the Tub: After the drainage has been completed, refill the hot tub with water, adding chlorine or bromine before testing the water chemistry with a test strip.

Preventing Biofilm Formations

Preventing biofilm formations can be difficult since you don’t have X-ray vision like Superman to see whether they’re accumulating in your plumbing system. But you don’t have to be if you follow certain processes on a regular basis. Here are the most common biofilm formation prevention techniques:

  • Change the tub water at least 3-4 times a year in regular intervals.
  • Check and maintain water chemical levels on a regular basis.
  • Change the hot tub’s filter cartridge twice a year. You’ll be surprised how much of a beating these cartridges have to take to sanitize and clean your tub water.
  • Every time you drain your tub, leave it dry and empty for a few hours so the plumbing system has a chance to dry, significantly decreasing the chance of biofilm formation.
  • Purge the plumbing system at least twice a year to clear out early biofilm formations.

Most of these preventative methods are something any responsible hot tub owner will do, except for the purging of the plumbing system. Doing so is not only good for your hot tub but the plumbing systems fitted with the other water sources as well, like taps.


1. Is hot tub biofilm harmful to humans?

Yes, hot tub biofilms are harmful to humans and can cause a wide range of skin and health problems due to the presence of bacteria that can harm the skin.

2. Does vinegar kill biofilm in hot tubs?

Yes, vinegar is surprisingly effective at killing biofilm formations in hot water tubs due to the disinfectant properties that vinegar has.

3. What’s the best biofilm cleaner for hot tubs?

There are many biofilm cleaners like the Hot Tub Serum an EPA Registered Weekly Maintenance Bio-Cleaner which are effective in cleaning and getting rid of the biofilm from your hot tub. Otherwise, you can go for other methods such as shocking with chlorine or using vinegar.

Final Thoughts

Biofilm formations are the sneakiest hot tub hazards you can encounter, so you need to be prepared accordingly. Knowing how to spot them by sight will help make things much easier for you when treating your hot tub. But as the old saying goes, prevention is better than cure, so taking steps to prevent biofilm formations is the best way to stay free from the health hazards they bring to your hot tub.

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I am Donald M. Beyer and I am backyard enthusiasts. I am a homeowner who has been doing DIY projects in and out of my house for many years. From simple backyard lunches to making an old-school pizza oven in my own backyard, I have a lot of experience in turning my backyard into my and my family’s personal playground.

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