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What Causes Slime in a Hot Tub? – How to Fix Slippery Water

Owning your own spa isn’t always a walk in the park. To keep your spa clean and healthy, you’ll need to stick to a strict maintenance routine, which isn’t too difficult once you find a rhythm but can quickly spiral out of control if you find yourself slacking off!

One of the more common problems brought to our team by hot tubbers is the appearance of hot tub slime (AKA hot tub biofilm or scale), a particularly nasty issue with a few root causes. We’re here to tell you everything we’ve learnt about these gunky buildups during our ten years as the internet’s leading inflatable hot tub guide to help you get rid of this stuff for good! 

If you’re asking, “What causes slime in a hot tub?” 

Here’s everything you need to know! 

Why is my Inflatable Hot Tub Slimy?

a pair of feet in a jacuzzi

If you’ve had a jacuzzi or hot tub for a while, chances are you’ve encountered that slimy feel or oily hot tub biofilm buildup; it’s just par for the course when you’re dealing with such a delicate ecosystem. Whilst hot tub slime can become harmful if left untreated, understanding the root cause of the issue will help you get rid of any gunk ASAP. 

So what are the common causes?

1. Biofilm

Hot tub biofilm growth occurs when the skin oils, cells and other organic contaminants left by bathers in a hot tub or swimming pools begin to mix with the bacteria and microorganisms in your hot tub water. This creates a slimy layer of film that often lurks inside the spa’s plumbing system.

Hot tubs present the ideal warm and moist environment for these bacteria to thrive, especially inside the hot tub’s plumbing, where the water is less likely to be drained and cleaned regularly. 

The slime you feel is a protective layer of mucus produced by these microorganisms resistant to pool sanitisers like chlorine and bromine, making getting rid of this slime an increasingly tricky challenge! 

2. Mould or algae

Another common cause of that biofilm feeling in your hot tub water is an infestation of mould, mildew or algae. It’s usually pretty easy to spot these contaminants lurking in your hot tub spa, as they’ll generally grow towards the water’s surface, forming a black or green-tinted layer of gunk. 

Mould and/or algae growth will most likely be caused by not adding the right amount of Chlorine sanitiser to your spa water or occasionally due to damaged filters not doing their job properly, so making sure to regularly clean your hot tub (including the filter) and balance your pH level is the best way to prevent these water contaminants from becoming an issue!

If you know, it’s a mould issue. Then learn how to get rid of black mold in a hot tub and have it looking pristine again in no time.

3. Scale build-up

If you live in an area with a hard water supply, chances are you’re sick to death of chalky scale messing up your plumbing! Hard water causes issues in hot tubs as its high mineral content can lead to deposits of white scale forming along the pipes, pumps and jets inside your spa.

Hard water will become more of a problem if your spa water’s pH and alkalinity levels are not kept within a range of 7.2-7.8. The more alkaline your water is, the more minerals will build up, so to prevent this chalky nuisance, keep on top of those ph levels!  

4. Chemical imbalance

Funnily enough, your hot tub or spa may feel unpleasant if you’ve simply used too many chemicals when treating your spa water! Balancing hot tub Chlorine sanitiser levels is a delicate art; we all get it wrong every now and then, so we’re betting most of you are aware of this particular slimy feeling. 

A chemical buildup of Chlorine or Bromine can make your hot tub spa feel unpleasant to soak in, so make sure that you’re accurately measuring your sanitisers when keeping the water balanced, and remember to use test strips to get a visual read on your chlorine levels and ph levels! 

5. You have a filtration issue

a couple of filters

Hot tub filters really are the heart of the machine! 

No matter how well you maintain your chemicals and sanitiser levels and try to manually prevent debris from entering the water, some nasties are always going to find their way into your jacuzzi! 

This isn’t so much of an issue as long as you have proper circulation through a clean filter, but the more work your filter does, the less effective it becomes. 

Most cartridge filters can last a couple of months before replacement jacuzzi hot tub filters are needed. Still, if you’re not rinsing your filter with water weekly, it can become clogged and ineffective, so it’s not unlikely that you’ll start to see a buildup of scum, slime or biofilm in the water!

This page explains the best way to clean hot tub filters

Another Less Likely Reason

Too many borates

These chemicals can be a convenient tool when attempting to balance a hot tub with precarious pH levels. They can reduce the amount of Chlorine you need to use and help soften the water inside your hot tub.

This is all pretty great, but water treated with borates is known to feel slippery and even a little greasy to the touch, so if none of the above issues seems to be the source of your slime problems, we recommend cutting back on your borate usage.

How to Get Rid of Biofilm in a Hot Tub Without Draining

someone spraying a cleaner

Now we know the most likely causes of your slimy spa tub, it’s time to look at the best ways to get rid of the underlying issues to help you get back to soaking in heal thy water as quickly as possible.

Buy a biofilm cleaner.

The best way to get rid of hot tub biofilm is simply to buy a specialised biofilm cleaner. 

Hot tub biofilm is a particular nuisance as the slime itself is resistant to your usual sanitising chemicals, so the only way to effectively break it down is to use an oxidising chemical cleaner. 

Unlike do-it-yourself products, these solutions will disintegrate the outer layer of slime that holds the bacteria together, allowing your Chlorine or Bromine sanitisers and chemicals to work correctly again. 

Just add some biofilm cleaner to the hot tub water and run your pump for an hour to ensure a deeper clean that can break down the biofilm not only on the visible surfaces but lurking within your hot tub spa’s pipes, filter and plumbing.

Here is a quick guide on what to clean a hot tub with.

Filter change: check, clean, or replace

If you want to prevent biofilm from coating your hot tub surfaces after a dose of chemical cleaner, you’ll need to pay particular attention to your hot tub’s filter! 

If this part of your spa still harbours any biofilm or bacteria cells, the water circulating through it will simply cause the issue to flare back up again.  

Remove your filter cartridge and check for any dirt or damage; if there are any tears or large deposits of gunk, just replace the filter. If the cartridge looks salvageable, simply soak it in biofilm cleaner overnight before rinsing with warm water and reinstalling it into your spa.

Empty and Refill the Hot Tub

The most reliable way to get rid of a biofilm infestation is simply to completely drain, clean and refill your hot tub spa with fresh, uncontaminated water. 

If you’re choosing this method, you should be aware that biofilm will lurk in hot tub plumbing and other unseen areas of your spa, as well as on the surfaces you can see. 

To ensure that you’re fully eliminating the bacteria, it’s best to pump some biofilm cleaner through the plumbing once your freshwater has been added! 

This page discusses how often to do a hot tub water change.

How Do I Keep Biofilm Out of My Hot Tub?

someone holding green slime

As with most aspects of general maintenance, the best way to avoid biofilm and slime issues is to prevent them from taking hold in the first place. It might extend your daily maintenance routine a little, but it will stop you from asking, “why is my hot tub slimy?”.

Maintain your filtration system

The best way to prevent hot tub biofilm from becoming an issue is to keep on top of your filtration system. 

This aspect of your hot tub spa’s operation is your best friend, so make a habit of rinsing and sanitising your filter cartridges as often as possible. Also, make sure to regularly check the pH level of the water to effectively kill bacteria and prevent algae and mould from forming.

Also, most modern spas (including inflatable hot tubs) have a dedicated button on the pump to engage a quick filtration cycle. Make use of this on a daily basis to help maintain a healthy water quality inside your spa.

Encourage showering before use.

Slime and biofilm will become more of an issue if your spa water is full of contaminants like skin cells, body oils, hair and lotions. Perfumes, deodorants and any other santizer you apply can also affect the balance due to the chemicals in those products.

By sticking to a routine of showering before taking a dip in your hot tub, you’ll drastically reduce the amount of these contaminants in the water, helping to prevent slime, gunk and biofilm from taking hold! 

Is Hot Tub Slime Dangerous?

an image saying health risk

Biofilm isn’t just uncomfortable and unsightly problems. These masses of bacteria and germs can be pretty harmful to the people using your spa and the hot tub itself! 

Will It make me ill?

As the sanitisers in your spa break down whilst tackling biofilm, they’ll often cause the water in your hot tub to become more acidic, resulting in skin rashes and other forms of irritation.

The bacteria and germs present in the biofilm can also lead to ear, eye and respiratory infections, especially if you’re running hot tub air jets, as this will create bacteria-ridden airborne contaminants!

Other health issues include folliculitis (which can require antibiotics to treat!) and even legionnaires disease, so we don’t recommend risking a bath in biofilm-infested hot tub water. If you do encounter these, try to find a hot tub rash cure immediately and ways to prevent it from happening again in the future.

Will it damage the spa?

In short, yes! Scale, in particular, wreaks havoc along the pipes and plumbing inside hot tubs, gradually building up to form hard blockages in the tub that prevent the filtration system and jets from working properly. 

Biofilm and bacteria infestations will also cause the water in your hot tub to become dangerously acidic, posing a risk to your health and damaging the surfaces and components inside your tub.

Slimy water may also clog up your hot tub filtration system, preventing debris from being filtered out of the spa water, or causing it to become stuck inside your hot tub’s filters. So for the good of yourself and your expensive hot tub, it’s best to remove algae, biofilm and scum ASAP! 

Never Ignore Water That Feels Slippery Or Greasy

Hopefully, the answer here is pretty evident by now. If the hot tub water feels greasy it can pose some serious risks to humans and hot tubs. Ignoring the issue will only make it harder to fix in the long run, so do yourself a favour and start sticking to that maintenance routine before hot tub slime becomes a real issue! 

More General Cleaning Advice

This page is about slimy hot tubs. For more ways to clean portable hot tubs, it’s here, whilst we have lots of articles for hot tub guidance from cleaning and buying to general maintenance.

Last Word

a full hot tub on some decking

With that, you should be all caught up on the causes, problems and fixes relating to hot tub slime, biofilm and the other nasty gunks that often plague mild-mannered hot tubbers! 

If the water inside your hot tub is starting to look a little goopy, you notice a chemical smell, or you can feel a slimy residue creeping in during your soaks, check for the most likely cause and don’t wait around to tackle the issue.

Consider the sanitisers you use to keep your hot tub clean, whether you have a hard water supply, how often you change your filters and whether you shower before taking a dip. 

Remember that preventative measures will save time and money; draining, cleaning and replacing the water is your best bet if all else fails. Follow all of these procedures and we hope you’ll never see biofilm again! 

John Devlin

Hello, Welcome to my website. I’m John, and I created the InflatableHotTubGuide while researching these spas nearly a decade ago. Since its creation, the site has become the leading UK resource for many models. As a passionate hot tub user, I love to test and explore all the latest machines this industry keeps creating. I hope you find our content helpful.