Why is my pool green?

Swimming pools can turn green for at least three reasons. Here's how to know what happened to yours.



Green water is no fun, especially if it's cloudy. Green pools are usually caused by an algae outbreak, but not always! There are three reasons that we know of for pools turning green:

  1. Algae outbreak (eutrophication of the water)
  2. Copper oxidation and oversaturation
  3. Imbalance of calcium and alkalinity (too much TA relative to CH)

How to identify the cause of green water

Start by doing the white bucket test. It takes only a minute or so.

white bucket test

Take a clean white bucket and grab a scoop of green pool water. Add about an ounce of liquid chlorine to the bucket and stir. Within 30 seconds, the color likely changed. If...

  • ...the water clears up, it was algae (or something organic, like tannins).
  • ...the water gets darker green, it was copper.
  • ...the water does not change color at all, it is likely an imbalance of TA and CH.

How to fix a green pool

Without going into too much detail here, see our green pool cleanup procedure (for algae outbreaks), and read this article about the water turning green from copper.  Finally, if you have too much alkalinity relative to your calcium hardness, correct your chemistry to have a minimum 3:1 ratio of calcium to total alkalinity that keeps your LSI balanced. Aim for 4:1 or higher.

We have seen green pools turn blue in minutes simply adding chelated calcium with acid blended in the same bucket (or Orenda Startup Barrel™). Correcting the CH and TA imbalance is very similar to the post-fill Orenda Startup process.