What is biofilm and how to prevent it

hot tub biofilm

What is biofilm?

Biofilm is a slimy film of bacteria that attaches itself to hard surfaces such as your hot tub’s plumbing. Biofilm is sometimes referred to as “hot tub slime” and can be difficult to remove. Biofilm is challenging to remove because even high chlorine content cannot penetrate its protective outer coating.


Signs of biofilm

  • Increased use of chemicals
  • Difficulty keeping the water clear and/or hot tub foam
  • Unpleasant and unusual odour from the water
  • Discoloured, oily bubbles, especially around your filters
  • Large white flakes (small flakes can be calcium)

    Pro Tip: If you have white flakes and aren’t sure whether it’s calcium or biofilm, do the following test.

    1. Fill a cup with water (including some flakes) from your hot tub (around 250 ml).
    2. Add roughly ½ teaspoon of bleach to the cup and stir.
    3. Wait 30 minutes.

    If, after 30 minutes, the white flakes have dissolved, you likely have biofilm, and if not, it’s likely calcium scale buildup.

Why does biofilm occur?

Biofilm (and bacteria in general) thrive in dark, hot (>90°F) water with organic materials from bathers. Bacteria like to attach to surfaces, and normally sanitizer (chlorine or bromine) will quickly destroy them. However, when free sanitizer levels fall below the minimum recommended levels (1 ppm chlorine; 2 ppm bromine), bacteria can begin to grow. This bacteria can form a protective layer within hours or even minutes and become biofilm.


Bacteria have reproductive cycles as short as 20 minutes – meaning if you leave your hot tub overnight with no disinfection, you’ll be dealing with billions of times more bacteria than when you exit the hot tub the night before.


How to get rid of biofilm

Removing biofilm from your hot tub requires using a plumbing cleaner like Ahh-some Tub cleaner. Add a tablespoon of your sanitizer (chlorine or bromine) and follow the directions on the product. You don’t need to balance your water to use Ahh-some Tub cleaner.


Wipe down the inside portion of your hot tub cover and the hot tub above the waterline. Clean your filters thoroughly (or leave them in chlorinated water for 72 hours). Make sure to add sanitizer to your hot tub as soon as you fill it back up.


Biofilm can be challenging to remove, and more than one cleaning may be needed.


How to prevent biofilm

Ensuring your hot tub is never left without sufficient sanitizer is the first and best defence against biofilm. Recommended free sanitizer level is between 3 and 5 ppm.


If you’re looking to go even lower than that, ensure you’re using an enzyme product like Spa Solution and/or a mineral cartridge like Jacuzzi ProClear or Nature2, and slowly reduce sanitizer while observing results. Remember to never go below 1 ppm, even with these other products.


Enzyme products like Spa Solution will also help break down oils and other contaminants that can help biofilm grow and may even help to break down the protective slime layer of biofilm. We highly recommend trying Spa Solution if you’ve experienced biofilm.

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