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How to control Green water algae in a planted tank

May 20, 2020 1 min read

How to control Green water algae in a planted tank

This form of algae is also known as "green pea" soup. The water turns into a cloudy green colour.

Common Cause

The primary cause is excess ammonia coupled with strong light for extended periods. This may occur particularly in new tanks / planted tanks that are not biologically mature. It often results from over-feeding, high levels of livestock waste and/or plant decomposition. It is more common in very warm tanks (80f+).


  • Some mild cases disappear on their own as the tank matures
  • Immediately lower light intensity (by increasing the distance of the light source from the tank or adding shades) and reduce lighting-period to 5 hours until problem disappears
  • Mild cases can be cured by over-dosing APT Fix(with care) or by using Purigen as filtration media
  • 4 - 5 day blackout for serious cases
  • Use Diatom filters
  • UV steriliser is a 100% cure for serious cases

For detailed steps on how to cycle a tank, click here

Green Water Algae