What Keeps Turning My Fresh Water Fish Tank Green?

Freshwater fish tank water can turn green if too much algae is present. Cleaning fish tanks once the algae has set in can actually cause the algae to return with a vengeance. Light triggers algae growth, so avoid setting your freshwater aquarium in front of a window or in a sunny area. Aquariums experiencing green water problems can be helped by placing live plants within the water after blacking out the tank for three days.

  1. Sunlight

    • Fish tanks set in front of windows or in sunny areas can experience green water problems, chances are, it is receiving too much light. Check the amount of light the tank is receiving. Move the tank away from a window or cover the back of it with a tank backdrop liner to block sunlight. You can also block all light from the tank for three days by wrapping it in foil or dark towels and allow it to reset. Algae is an indication of excess nutrients in the aquarium, which is not harmful to the fish, but it can be visually unsightly.

    Plant Life

    • Tanks with green water could experience a high algae count when the tank has no plant life. Many fish tank enthusiasts place plastic plants within the tank, thinking they are easier to care for, which is a common misconception. Live plants actually use the nutrients the algae are using within the tank, thus lowering the algae growth. Place live plants in the tank that work well with the fish already inhabiting the tank or that you plan to place in the tank. If you have schooling fish, refrain from using tall plants that could spread out over the surface of the water because many schooling fish enjoy having room to swim or feed at the surface.

    Artificial Light

    • Check the aquarium's light bulbs. Bulbs for color-enhancing aquariums are not the same as bulbs for growing aquarium plants. If you are unsure which bulbs your aquarium has and your aquarium has a green water problem, switch out the bulbs to be on the safe side, to ensure the bulbs are for aquarium color enhancement. Turn the bulbs off during daytime hours and during the night when you are asleep and are not enjoying the aquarium, to make sure the water isn't receiving too much light. Use a light timer when away from home.

    Improper or Non-functioning Filters

    • Check the filter system within the aquarium if your water turns green. Green water indicates an algae bloom. You can wait it out and the water could eventually fix itself, or you can change 20 percent of the water out of the tank. Refrain from changing all of the water at once because this action will kill off all the algae at once and cause an imbalance that isn't healthy for the tank. Do not rinse filters out with tap water and then place them into your tank.