What Causes Hot Tub Biofilm? (and how to get rid of it)

what causes biofilm lg

You don’t need to be a chemist to own a hot tub, but for your own safety and those soaking in your hot tub, knowing what chemicals to use and how to maintain it is crucial. Biofilm is one thing to be aware of, but what causes hot tub biofilm?

Here’s what I’ve seen:

Biofilm in a hot tub is caused by excess contaminants on the skin and bathing suits of people soaking, in addition to airborne contaminants. It is essentially a collection of bacteria that builds up in the plumbing and equipment of the hot tub. But it is rarely seen, so many are not even aware they have it.

But it’s not just that simple.

And what’s more, you’ll want to know how to get rid of it and how to prevent it from forming in the future.

In this article, I will explain exactly what biofilm is and why you and your family and friends are the biggest contributors to it.

Let’s get into it.

Ready to Spend Less Time On Maintenance and More Time Enjoying Your Hot Tub?

Let’s face it. Balancing the water, cleaning filters, dealing with rashes, and trying to figure out which chemicals to buy and add can make you feel more like a chemist than someone who just wants to relax after a long hard day!

That’s exactly why The Hot Tub Handbook and Video Course is so valuable!

This is from Matt over at Swim University and he developed it for people looking to save money, time, and frustration. His tips on chemicals can save you $100/year just by making sure you buy only what you need.

So if you’re ready to stop being confused or frustrated with your hot tub and start spending more time in it, check out The Hot Tub Handbook and Video Course.

Just click that link to learn more on their website.

Why does my spa feel slimy?

A hot tub or spa may feel slimy if biofilm is present in the water. Slime is the outer layer that clings to bacteria and microorganisms to protect it from whatever sanitizer is used to keep the hot tub clean. This can make biofilm impervious to normal sanitation measures.

Slime in a hot tub is a sure sign that your water is in poor condition, and you need to act fast to rectify the situation.

Slime builds up when the filter isn’t doing its job, so the first thing you need to do is take it out and clean it. You should clean your filter every 3 weeks at least.

It’s just a case of hosing it down and getting into the folds. I recommend the Filter Flosser from Amazon for this, which simply connects to your garden hose.

Then you need to check your pH and alkalinity levels to make sure these are in balance. This should be done every other day or before getting in if you haven’t used your tub in a while.

You should also add sanitizer every 2-3 days on top of using chlorine or bromine every 3-5 days. And shock the water once a week.

If you use chlorine and you’re new to the world of hot tubs but not sure how much chlorine you need to add, this recent article will be of great value to you. After all, too much chlorine can actually be worse than not enough.

You can read it here on my website by clicking on the link.

What does biofilm look like?

Biofilm itself is rarely, if ever, seen as it primarily builds up in the pipes and equipment of a hot tub. But if slime is present around the edge of the waterline, that iss more than likely biofilm.

The slime encases the biofilm, making it difficult to get rid of because the sanitizer that normally attacks the biofilm cannot penetrate the slime.

Biofilm is the residue from body lotions, deodorant, sweat, and other organic matter that finds its way into your tub.

Usually, the filter collects most of this stuff, but if this is clogged, it will stay in the water and stick to the surfaces of the hot tub.

One of the best ways to prevent biofilm is to shock the water weekly. 

Shocking is the process of giving a high dosage of chlorine or non-chlorine chemicals to reactivate the sanitizer by increasing the available free chlorine in the water. But it won’t kill biofilm if it’s already present. (More on that below).

After adding chlorine to your hot tub, you should wait a while to allow the chlorine to dissipate. But how long does that take?

See my recent article if you want to know more about this. After all, the wait times vary depending on whether you are talking about shock or sanitizer. Also, liquid vs. powder vs. a floater all vary in wait times considerably.

Just click that link to read it on my site.

Shocking should be a part of your maintenance program anyway. For regular use, say 2 or 3 times a week, shocking the water every 7 days is sufficient.

Can hot tub biofilm make you sick?

Biofilm is full of bacteria, and this can make anyone who soaks in the hot tub sick. So anyone getting into a hot tub that is smelly, cloudy and slimy, is taking a risk.

The most common symptoms are rashes, itchiness, and tender skin, which disappear after a day or two. But if the symptoms persist or you start to get sores forming, this is a sign of something more serious.
It could be folliculitis – a type of bacteria that thrives in the warm water of a hot tub that isn’t properly sanitized.

In a recent article, I discussed how to get rid of folliculitis. Folliculitis is often mild, but extreme cases will require antibiotics. So knowing what to look for and how to get rid of it is crucial!

Just click that link to read it on my site.

But it’s not just skin problems that biofilm causes. Biofilm can also result in ear, eye, and respiratory infections. As the bacteria mixes with the bubbles from the jets, they get aerated and rise as tiny droplets that can be inhaled or enter your ears and eyes.

In extreme cases, Legionella and Urinary Tract Infection (UTI) can result from spending time in a hot tub that hasn’t been well maintained.

What are the signs of biofilm in a hot tub?

A biofilm buildup in a hot tub will show some or all of the following signs: bad smells, cloudy water, excess foam, or slime. 

But a bad smell may also be caused by poor sanitation. Adding chlorine or bromine to the water regularly will solve this.

If you use chlorine as a sanitizer, this can mix with the biofilm to form chloramines, and this will give off a strong smell of chlorine when you lift the lid. Don’t make the mistake of thinking this is a sign of healthy water – it isn’t!

Similarly, if you use bromine, the biofilm can react with this to form bromamines, creating a caustic or chemical smell.

But just adding sanitizer and shock regularly doesn’t really get rid of biofilm. (More on that in the next section).

Foam on the water’s surface can be a sign that the water is getting full of Total Dissolved Solids (TDS). And allowing that to go unchecked can eventually lead to biofilm.

All of these symptoms are caused by bacteria that lurks in the biofilm, and I discussed how to get rid of bacteria in a recent article.

Just click that link to read it on my site.

How do you get rid of biofilm in a hot tub?

The best way to get rid of biofilm is to use a biofilm cleaner every 3 months when the water is being changed. This will eliminate any residual biofilm buildup and clean out the pipes and equipment so the freshwater being added will remain bacteria-free.

My favorite product for this is Oh Yuk! Healthy Hot Tub Cleaner on Amazon – you can check out the current price on Amazon by clicking on the link.

Before you drain the tub, remove the filters.

Then add 8 ounces of Oh Yuk to the water and turn on all the jets and water features to allow the water to circulate for an hour. You’ll have to manually restart the jets as they will likely time out after 15 minutes.

This will get right into the places you can’t clean manually, like the pump and plumbing system.

Then, cut the power, drain your hot tub and wipe down the surfaces with an all-purpose cleaner such as Windex, or if you already have some in, white vinegar is as good as anything else out there.

As a rule, if you are using chlorine or bromine as a sanitizer, you should change your water every 3 months, depending on usage, and if you use Oh Yuk every time, you will not have a problem with biofilm in the future.

CLICK HERE to check the current price of Oh Yuk! On Amazon.

Another preventive thing you can do is to make sure everyone showers before getting in the hot tub to wash off all those deodorants, perfumes, and sunscreen.

Did I cover all you wanted to know about the causes of hot tub biofilm?

Biofilm is caused by the residue of all those things you bring into the hot tub.

That includes deodorants, oils, perfumes – and the things that fall in, such as bugs and leaves. It is a natural process, and as a hot tub owner, you have to deal with it.

But it is not so much the biofilm that’s the problem. It is the bacteria that resides inside it!

In this article, you will have learned how to recognize biofilm, how to eradicate it, and how to prevent it from occurring again. I hope this covers everything you wanted to know, but if there is something that I missed, just drop me a line.

Ready to Spend Less Time On Maintenance and More Time Enjoying Your Hot Tub?

Let’s face it. Balancing the water, cleaning filters, dealing with rashes, and trying to figure out which chemicals to buy and add can make you feel more like a chemist than someone who just wants to relax after a long hard day!

That’s exactly why The Hot Tub Handbook and Video Course is so valuable!

This is from Matt over at Swim University and he developed it for people looking to save money, time, and frustration. His tips on chemicals can save you $100/year just by making sure you buy only what you need.

So if you’re ready to stop being confused or frustrated with your hot tub and start spending more time in it, check out The Hot Tub Handbook and Video Course.

Just click that link to learn more on their website.


Image by mcmurryjulie from Pixabay and Image by VIVIANE MONCONDUIT from Pixabay

Jeff Campbell

Jeff Campbell is a husband, father, martial artist, budget-master, Disney-addict, musician, hot tub lover, and recovering foodie having spent over 2 decades as a leader for Whole Foods Market.

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