Algae is one of the biggest problems in pond and aquarium maintenance. There are over 17,400 species of algae, most of which are a type of plankton algae or filamentous algae. Algae may turn the water green, suspend in the water, or exhibit itself in the form of green strings or scum on the water's surface. Algae needs sunlight and nutrients to grow; many aquariums and ponds contain excess nutrients that allow algae to thrive. If you leave an algae problem uncontrolled, the algae can quickly take over. Natural algae removal methods are best for maintaining the health of fish.
Skim the surface of the water with a net to remove as much surface algae as possible.
Brush the sides of the tank with a sterile brush or pond vacuum so the algae can be circulated through the filter with the water. Stir or vacuum the gravel on the bottom of the tank so it can move through the filter.
Add algae-eating fish and other aquatic animals to help keep the water clean. Hermit crabs and snails will eat almost anything in the water; sea cucumbers live in the sand bed and circulate the sand to keep algae from settling.
Add surface and shade plants to the pond or tank to compete with the algae for nutrients. Surface plants also shade the water to inhibit new algae growth.
Remove fish tanks from direct sunlight and turn off the aquarium light when you are not looking at the aquarium. Algae cannot thrive without sunlight, but remember that other aquarium plants won't be able to thrive either.
Feed your fish less food to limit the amount of available nutrients in the water. Algae will grow rapidly in water with excess nutrients.
Scale down your number of fish to reduce the nutrients in water from fish waste. As a general rule, you should have no more fish than can fit from nose to tail across the widest point of the tank or pond.
Add barley straw, extract or pellets directly to the water according to package instructions. These will remain active in the tank for months, helping to inhibit the growth of algae.
Add a nitrifying bacteria to feed on the excess nutrients and starve the algae. These can be found at any pet store that sells fish and aquarium supplies.
Sterilise a scrub brush by soaking it in a bleach and water solution for two minutes, then rinsing it with cold water and allowing it to dry.
Ask an associate at a pet retailer before using any chemical algae removal products to make sure they won't kill fish.