Why is hot tub green

If you open your hot tub to find green water then it is not only unpleasant, it prevents you using your hot tub safely and it suggests some sort of chemical imbalance. In this post we will explain why hot tub water goes green, what causes it, what to do to fix it and how to prevent your hot tub water from going green again.

What Makes Hot Tub Water Turn Green

Lack of Sanitiser in the Water / Algae Growth

It is most likely that there is not a sufficient level of santisier (chlorine or bromine) in the water and as a result algae is starting to grow and form in the water. This may be due to lack of attention to the water over a long period, heavy usage which has resulted in the sanitiser dropping quickly and/or something affecting the sanitiser efficiency dramatically. You can read more about a lack of chlorine in your hot tub here.

Excessive Metals

If your sanitiser levels are balanced to 3-5ppm and you still have a green tint in the water then it may be excessive metals in the water. Metals in the water can be taken in by the source water or can be from spa components and when they react with the water, they can leave a green tint. 

How to Clear Green Water from a Hot Tub

Shock the Water and Clean Filters

To clear green water, you need to kill off the potential algae growth and give the water a good clean to try and bring it back to a level where normal sanitiser levels can be maintained at 3-5ppm. Dose with chlorine or bromine granules to bring the free chlorine or total bromine level above 10ppm, this will be around a 50g dose for a 1,000L hot tub. Ensure you leave your cover off for at least 20 minutes after this dose as the high level of chlorine can cause damage to pillows and cover burn. 

After a few hours, you should start to notice it clear. At this point, it is worth cleaning your hot tub filters to ensure any dead Algae is removed from the water.

Drain and Refill

If the water is not able to be recovered using the above method and you want to start again, then you have the option to fully drain and refill with fresh water. When doing this, add chlorine to a level of 5ppm, wait 1 hour then use a pipe flush to clean out the pipework. This will ensure you combat the algae that may be lurking in the pipework.

If you are concerned about metals in the water, use a pre-filter such as the Hot Spring Clean Screen to remove metals from source water, eliminating the potential for a green tinge from metals to form in the water.

Tips to Prevent Green Water in a Hot Tub

  • Ensure your levels are always within range - Chlorine/Bromine 3-5ppm. PH 7.2-7.6. Alklainity 80-120ppm.
  • Use a pre-filter when filling if concerned with metal content in the water.
  • Keep you filter clean and degreased using a filter cleaner. Filtration assists with sanitisation. 
  • Drain your hot tub every 3-4 months and use a pipe flush to remove biofilm.