Green water
The whole tank turns pea-soup green.
The water itself turns green and cloudy, so you cannot see across the tank. The cause is a bloom of floating single-celled algae.
- Main cause
- Direct sunlight or too many hours of strong light
- First fix
- A blackout of several days with the tank covered, often three to five, can clear it, though results vary.
In a real tank: green water in a planted tank. Photo: Russel Leidich/dangerousfishbowl, CC BY 3.0, via Wikimedia Commons
What causes it
- Direct sunlight or too many hours of strong light
- Ammonia or excess nutrients, often in a new tank or after overfeeding
- A tank near a window
How to remove it today
- A blackout of several days with the tank covered, often three to five, can clear it, though results vary.
- An ultraviolet (UV) sterilizer on the filter usually clears it, often within days.
- Water changes alone rarely clear it: the algae regrow from what is left.
How to stop it coming back
- Keep the tank out of direct sunlight and put the light on a timer; 6 to 8 hours a day is a common starting point.
- Test ammonia and feed less.