Controlling Algae Growth in a Pond


An established pond will most likely experience algae growth at some point. Moderate amounts of some forms of algae are actually healthy for the overall pond ecosystem, but maintaining control over that amount is important. Excessive algae can rob your pond of oxygen, causing fish illness or worse, fish death.

Algae are simple structured plants that have no root systems, leaves or any of the other similar characteristics seen in higher plant species. The two most common types of algae are planktonic algae and filamentous algae.

Planktonic algae can be identified by green, blue-green, yellow-green or even red colored water, also known as a bloom.  Blooms can encompass the entire surface of a pond and resemble a pea soup consistency if left untreated.

Filamentous algae initially form around the perimeter and the bottom of the ponds in the spring in a mat-like fashion and take on the characteristic of being stringy. It’s common to see this type of algae on rocks and even waterfalls, making these surfaces slippery. These algae provide no real benefit to a pond’s ecosystem.

Algae thrive off of:

  • Excessive sunlight
  • Low oxygen-high carbon dioxide levels 
  • Excessive nutrients

Excessive Sunlight

Excessive sunlight helps to fuel the photosynthesis process, which also relies on carbon dioxide, and water.

Long Term Solutions: The main goal here is to allow less sunlight to enter the pond. One natural way to achieve this is to add shade bearing plants, such as lilies, to your pond. These plants can easily cover a large percentage of the water surface and will also offer a natural protection from predators for your fish. Another option is to add shade dye to your pond. This eliminates how much sun can penetrate the water, inhibiting the photosynthesis process.

Excessive Carbon Dioxide

Pond Aerator Application

Excessive carbon dioxide fuels the photosynthesis process.

Long Term Solutions: Increase oxygen levels by providing aeration. Air diffusers and waterfalls are some examples of ways to infuse oxygen into the pond. It’s also important to remove decaying plant life, as this robs oxygen levels.  We have a wide selection of aerators.

Excessive Nutrients

Excessive nutrients that help algae to thrive consist of nitrogen and phosphorus. Several sources for these nutrients are local phosphorus-rich fertilized areas, such as treated farm fields or yards, that wash into the pond. Other sources include nitrogen found in excessive uneaten fish food, decaying vegetation and fish waste.

Long Term Solutions: Eliminating or maintaining these nutrient sources properly will help alleviate that part of the problem. Clean all decaying vegetation from the water and only feed fish the required amount of food as recommended by the food manufacturer.  

Also consider adding beneficial bacteria, which will compete with algae for these excessive nutrients.  Beneficial bacteria will also help to maintain the entire ecosystem of your pond.

Please Note:  If a quick fix solution is needed to control algae, there are algaecide products available. Be aware that after treating your pond with these products, the decaying of the algae will result in additional oxygen loss due to the decomposition process. This can lead to fish kill. Always follow all instructions on any products you use.  Most, if not all, products will require you to use aeration along with their algaecide products to assure you are replacing oxygen back into your pond.