Algae is not only unsightly, but it can also grow until it suffocates your fish and plants. Just like other plants, algae needs light, nutrients and water to grow. So to control algae growth, you'll need to control these factors to stop algae growth. There are many natural ways to control algae, as well as chemical and filtration methods. Depending on the severity of your algae problem and whether you have fish or other plants in your pond, you can choose the right method for your pond to stop algae growth.
Control the light to stop algae growth. Minimize the amount of light that penetrates the pond's surface by adding floating and surface-dwelling plants, such as water hyacinths and water lettuce. You can also try adding submersed plants with large foliage that floats on the water's surface, such as water lilies and lotus.
Minimize the nutrients that algae needs in order to grow, including nutrients contained in rain water. Make sure all gutters and downspouts are not directed toward your pond to minimize the amount of rainwater that gets into your pond. Build a raised lip around your pond to keep rain runoff out of your pond.
Limit the amount of carbon dioxide in your pond to stop algae growth. Add to your pond some oxygenating plants that will use up the carbon dioxide before the algae can get to it. Elodea is a popular oxygenating plant.
Keep your filter clean and working properly. Clean your pond filter at least once every month to keep it free of debris. A clogged filter will end up killing the bacteria that grow to breakdown fish waste. Pond water that is not filtered properly will be full of nutrients which enhances algae growth.
Install a UV sterilizer. When the pond water is pumped through a UV sterilizer, the device kills any algae in the water.
Add an algaecide to the pond water. Liquid types of algaecides are very effective in killing algae but can also kill your pond plants. Be sure to read the label and use a liquid algae inhibitor that won't harm your plants.