Causes and Cures for Green Aquarium Water

Green Aquarium Water
Green Aquarium Water. Nat Tarbox

Other Names: Algae bloom

Color: Green tinted water

Appearance: The water itself turns green. In severe cases the water may be so green that the fish are not visible.


  • Suspended microscopic algae
  • Excess light, especially direct sunlight
  • Too many fish
  • Excess nutrients
  • Excess wastes
Green water is usually due to either a significant excess of light (particularly direct sunlight), or a major water quality problem.
Although it may look terrible, it is not toxic to fish.



  • Blocking out light completely
  • Diatomic or micron filtration
  • Introduce daphnia to the tank
Water changes will reduce green water temporarily, but will not eliminate it. Completely blocking out all light for three days or more is very effective. The use of a diatomic filter will remove the suspended algae. If daphnia are available, they will quickly eat the microscopic algae, then in turn be eaten by the fish.


Note: Water aggregators that profess to clump suspended algae and remove it are not effective against green water.


  • Regular water changes
  • Regular aquarium cleaning
  • Use of UV Filter
  • Avoid direct sunlight on tank
  • Avoid overfeeding fish
  • Do not overstock the tank
As with any algae, keeping the tank clean and performing regular water changes is one of the best preventative measures. Prompt attention to sudden algae growth will prevent more serious problems