What causes white flakes in a hot tub and how to get rid of it

When you notice white flakes in your hot tub’s water, it’s almost always one of two things:

  • Biofilm
  • Calcium scale


Biofilm occurs when your hot tub’s sanitizer (chlorine or bromine) drops too low, resulting in bacteria build-up in your pipes. When dealing with biofilm, the white flakes are often accompanied by an unpleasant and unusual odour, discoloured, oily bubbles, and slimy-feeling water. You’ll also likely have noticed an increased use of chemicals.


Calcium scale build-up is the result of hard water. Just as your kettle gets white flakes around its heating element, so does your hot tub. Calcium scale usually builds up in the hot tubs plumbing, and especially the heater, which eventually detaches and floats around in the water.


How to know if white flakes are biofilm or calcium

Follow these 3 simple steps to determine if you’re dealing with biofilm or calcium scale.

  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 build-up.


Preventing biofilm flakes

Read our article on biofilm to learn more about its removal and prevention.


Preventing calcium scale flakes

Preventing calcium scale is much simpler than dealing with biofilm. Read our article on calcium flakes to learn about its removal and prevention.

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