What causes green hot tub water and how to fix it

What causes green hot tub water and how to fix it

Finding green water in your hot tub can quickly derail your plans to enjoy your hot tub. Green water is usually an indication that your hot tub has algae. Fortunately, this is usually a quick fix. In this article, we’ll discuss what causes green water, how to deal with it, and how to prevent it from happening in the first place.


What causes green water

Green water is usually an indicator of algae, resulting from low sanitizer (chlorine or bromine) levels. It can be easy to forget to add sanitizer, especially if you haven’t used your hot tub in a while, and when levels start to dip below 1 ppm, algae and/or bacteria will begin to grow. If you’ve constantly been adding sanitizer to your hot tub, check if your pH levels are high, as this will make sanitizer disappear quickly.


Occasionally algae can enter the hot tub if bathing suits are contaminated (perhaps used in a lake) or due to phosphates (although this is uncommon).


How to clear a Green Hot Tub

Green water is often cleared up with sanitizer (chlorine or bromine). You can use the directions on the back of your sanitizer container to clear it; you may have to repeat this process more than once.


  1. Increase your filter settings to 24 hours.

    If you own a Jacuzzi:

  2. Rinse (or clean) your filters
  3. Test and balance your water (do not skip this step, or you may be wasting your chlorine or bromine)
  4. Brush up all algae from the seats, floor and walls of your hot tub - sanitizer won’t eliminate algae unless it’s free-floating in the water.
    • Use your hands and feet, a towel, a sponge (not the coarse - usually green - side), or a soft-bristled brush.
  5. Add 2 capfuls of Spa Shock and run pumps with the cover open for 20 minutes.
  6. Add 30g (2 tablespoons) of chlorine per 1000L and run pumps with the cover open for at least 20 more minutes.
  7. Re-test water in 6 hours (or next morning if adding sanitizer at night).
    • If sanitizer (chlorine or bromine) is 1 ppm or less, repeat steps 5 and 6.
    • If sanitizer is between 1 and 3 ppm, add 15g of sanitizer per 1000L and repeat step 6.
    • If sanitizer is between 3 and 5 ppm, add 15g of sanitizer.
    • If sanitizer is above 5 ppm, do a final test the following morning.
  8. Clear your filters with a filter cleaner (not just a rinse).
  9. The hot tub water will likely go cloudy-white - it will take time to filter out. Rising your filters daily or using Jacuzzi Spa Clear will remove the cloudiness faster.


The goal with the above steps is to add sanitizer until levels remain high for at least 24 hours - this indicates all the algae has been killed (and it just needs to be filtered out). You may need to repeat the above process several times.


Pro tip: the longer the hot tub has been at less than 1 ppm of sanitizer, the more you’ll use. This is because the algae that cause green hot tub water will grow back once sanitizer levels fall below 1 ppm. Don’t wait too long to re-test your water.


Once your hot tub goes cloudy, rinsing your filters daily or multiple times daily will help clear it faster. It can take up to a week for the cloudiness to fully clear, but there should be a noticeable difference in two days. When your sanitizer levels have remained high for 24 hours, you can add Jacuzzi Spa Clear to help remove the cloudiness faster (often in less than 24 hours).

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