Instructions
Control the amount of light your tank receives. While goldfish need six hours of light a day, too much light will encourage algae to grow. Keep your tank away from sources of sunlight, such as windows. Put your aquarium lights on a timer, ensuring they are not lit for more than six hours a day.
Change the water in your tank regularly. This will inhibit the buildup of potassium, nitrogen and phosphorous, things essential for algae growth. When changing the water in your tank, change half at a time. This will allow the goldfish to acclimate.
Put live plants in your aquarium. These consume nutrients in the water, like nitrate, that algae requires to grow.
Control the amount of food you give your goldfish. Any food waste will cause nitrates to build up, and algae to spread. If you see food waste in your tank, remove as much as possible with a net.
How to Stop Algae Growth On Goldfish
Algae is a common problem encountered by goldfish owners. It is caused by overexposure to sunlight, and too many nitrates collecting on the surface of the water. Too much algae can be damaging to goldfish and can harbor diseases -- some of which are fatal. If you have too much algae, it can spread to the fish themselves, leading to fungal infection. It is better to prevent algae growth, than to treat it, when it has infested your tank. But it can be controlled. If your tank is free from algae, your fish will be free from algae too.