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How to Control Pond Algae

It is very disheartening to see your pond filled with algae, which can suffocate the fish and aquatic plants. Here are some suggestions to control pond algae.
Gardenerdy Staff
Last Updated: Jul 30, 2018
There are two main types of pond algae - the planktonic algae or the filamentous algae. Planktonic algae are otherwise known as single cell or pea soup algae. They lend a green color to the pond water.
Filamentous algae are hair-like in appearance. In large amounts, they float over the pond, like a green mat. In small amounts, both these algae are beneficial for the environment of the pond. However, unrestricted growth of algae can ruin the pond ecosystem. Hence, it is very important to control the growth of algae in your pond.
The uncontrolled growth of algae in a pond may occur due to various reasons. The growth of algae depends on sunlight, sufficient amount of nutrients like phosphate and nitrate, and a higher pH level. The excess nutrients in the pond could be due to rotting vegetation, presence of fish feed or dead fish, and fertilizers leaching from nearby garden or lawn.
The rate of pond algae growth is higher during summers or when they get direct sunlight. The higher pH level of the water can be attributed to certain materials used in the construction of the pond.
Marble, limestone and concrete alter the pH levels of the pond water. Lack of pond filters can result in stagnant water that becomes ideal for algae growth. Lack of healthy aquatic plants in the pond can also lead to this menace. These plants feed on the excess nutrients in the pond, thus preventing algae growth.
Controlling pond algae can be started right from the time of construction of the pond. You can prevent the overgrowth and spread of algae through various methods. Some of them are given here.
  • A slope made at the deepest point of the pond facilitates collection of the debris, which can be removed easily.
  • A wall around the pond prevents the entry of run-off rainwater, which can increase the pH level of the pond water. This will help to control pond algae growth.
  • Abstain from using limestone, marble or concrete for constructing the pond.
  • Algae growth is normal in newly constructed ponds due to high level of nutrients. So, wait for a few weeks before adding fish. Fish can increase the nutrient content of the water.
  • The pond should have a minimum depth of 24 inches, to prevent sunlight from reaching the bottom. You can design the pond accordingly, to reduce the overgrowth of algae.
Algae Removal Boat
  • You may remove the algae manually, with a pump or soft brush. Add variety of aquatic plants to consume the excess nutrients. These plants should cover 50% to 70% of the surface area of the pond. Water lilies, water lettuce, water hyacinth are perfect for this purpose. You can use submerged plants like anacharis.
  • Add nitrifying bacteria to pond water. These bacteria can feed on the nutrients used by the algae for their growth. These can be grown on rocks and plants. You can also add a bundle of barley straw to the pond. Barley straw helps keep the water clear and odor-free. You can keep the straw submerged in water, but don't allow it to sink to the bottom.
  • Add some fish that feed on algae. This can also help to control pond algae growth to some extent. In that case, you should not overfeed the fish. Reduce their feed, thereby forcing them to feed on the algae.
  • A pond aerator or a fountain can increase the oxygen level of the pond, thereby energizing the bacteria, which in turn help in reducing the algae. These instruments can also facilitate better circulation of water and lessen the growth of algae.
  • Refrain from using tap water to clean the pond or for a water change. This can kill the beneficial bacteria too. Never go for a complete water change, which can result in a high rate of algae growth. Clean the bottom of the pond on a regular basis.
However, a pond does require algae in moderate amounts, but never allow them to grow uncontrolled. This can reduce the oxygen level of the pond, which in turn kills the fish too. Hence, controlling the growth of algae is important for a healthy ecosystem of the pond.