Biofilm Removal From Your Spa or Hot Tub

Over time the surfaces inside a spa and the plumbing can begin to accumulate excessive amounts of grime and bacteria called biofilm. Biofilm is a living organism, a slimy substance that is a combination of bacteria, dirt and organics.

Body oils, dead skin cells, lotions, cosmetics and more can become the base for biofilm, and then it begins to grow and spread on its own. It is most likely to develop in spas that do not have consistent water chemistry or have very high bather loads. It is usually found in areas of poor water circulation.

Biofilm is especially likely to develop in a spa that has been left with water in it without the filter system running for an extended period. If any moisture is left inside your plumbing, bacteria can thrive and spread. This is why biofilm is present in many jetted bathtubs as well. The bathtub is used and then drained, and the small amounts of water left in the jets contain the building blocks for biofilm.

Biofilm is resistant to sanitizers and difficult to remove. Cloudy water, foaming, and bad odors result, resistant to even heavy doses of regular and potent spa shock. If you have any of these symptoms, it is time to drain and thoroughly clean your spa.

Doing a deep cleaning on a regular basis will help to prevent biofilm from forming and is the best way to completely remove it once it is present.


How to Deep Clean Your Spa

1. Remove and Clean Cartridge Filter Element

Filter Perfect for cleaner spa filters

Since you are going to spend some time cleaning the inside of your spa and clearing out your spa plumbing, this is a perfect time to soak the cartridge overnight with a cleansing solution. Filter Perfect is a great choice. If you don’t clean the filter you are going to be running clean water through a dirty filter, allowing buildup to occur more quickly.

For tips and detailed instructions on how to deep clean your cartridge filter element, check out Martin’s post “How to Really Clean a Pool Filter Cartridge.” Remember that spa filters should be replaced after about 10-15 cleanings, which comes out to be once or twice per year for most people.

2. Purge Plumbing Lines

This step is what will remove built-up biofilm from inside the pipes in the spa. This is critical; biofilm will build up in plumbing lines over time, and if it isn’t removed, it doesn’t matter how clean the interior of the spa is because water is flowing through biofilm filled pipes and bringing bacteria back into the spa.

Before you purge the lines be sure to take out any removable spa pillows or any other accessories that might be in the spa; no need to coat them in purged biofilm!


By adding Spa Purge and allowing your spa to circulate overnight you will draw out built-up biofilm from the plumbing lines into the spa. If it is your first time doing this, or it has been a while, I think you may be surprised how much muck and yuck comes out when using Spa Purge.

3. Drain the Spa


Now that we’ve purged all of the gunk from the plumbing lines into the spa, we need to drain the spa and deep clean the surface. Check your spa owner’s manual for specific draining instructions for your model spa; they can all be a bit different.

Or you could always use a submersible pump, like the Water Wizard. This is quick and easy to use and will have most spas drained in a half hour or less, depending on the gallonage.

On average, spa owners drain and refill their spa about every 2-4 months. This can vary depending on the chemical balance in the water and how often the spa is used (and how many people are using it).

4. Clean the Spa

In The Swim Spa Care Cleaner

Once you’ve completely drained the spa you will clean the interior surfaces. A soft rag should easily remove dirt from the hot tub shell. Pay extra attention to the waterline where the most buildup will occur. Our Spa Cleaner is a great degreaser and will not leave behind any residue.

Spa Pillows can be removed and cleaned with a mild soap and water solution or you can use the Spa Cleaner. If you use a soap solution be sure to rinse the pillows off thoroughly to remove any soap residue. Since the rest of the spa will be sparkling, this is also a good time to condition spa covers with Cover Care.

In The Swim makes every effort to provide accurate recommendations based upon current ANSI/APSP/ICC-5 2011 (R2022) standards, but codes and regulations change, and In The Swim assumes no liability for any omissions or errors in this article or the outcome of any project. You must always exercise reasonable caution, carefully read the label on all products, follow all product directions, follow any current codes and regulations that may apply, and consult with a licensed professional if in doubt about any procedures. In The Swim assumes no legal responsibility for your reliance or interpretation of the data contained herein, and makes no representations or warranties of any kind concerning the quality, safety, or suitability of the information, whether express or implied, including, without limitation, any implied warranties of merchantability or fitness for a particular purpose.