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.