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How to Kill Pond Moss

lillies in a pond image by Jorge Moro from

Pond moss, also known as pond scum, is a fuzzy or stringy slimy green algae that forms in clumps on a pond's surface. Some algae in ponds is beneficial, providing food for fish and oxygenating the water. However, stringy pond moss is a nuisance because it looks bad, grows quickly and competes with fish and plants for light, nutrients and oxygen. In most cases, a sudden bloom of pond moss indicates a deeper imbalance in the pond's ecosystem. Taking preventative steps is the best way to kill the algae and prevent future blooms.

Remove Pond Moss

Remove the pond moss physically when it blooms and floats to the surface. Use a rake, broom or your hands to clear away the algae and dispose of it elsewhere.

Clean organic debris from the bottom of the pond with a pond vacuum. This is especially important in the spring, when leaves, twigs and other organic materials from nearby trees begin to rot. Rotting organic material provides nutrients to the algae and helps it grow.

Add nitrifying bacteria tablets to the water. These are available from pond supply stores, and they contain micro-organisms that eat pond scum and help keep it in check.

Use barley straw to naturally remove and control algae. This straw is available at garden supply or pond supply stores. As it decomposes, it releases chemicals that prevent the growth of new algae.

Prevent Pond Moss

Check your pump to make sure it's running an adequate amount of water through the filter. As a rule of thumb, the pump should move half of the total volume of the pond every hour. Keep the pump running at all times.

Install a skimmer to clear organic material from the surface of the pond, or clean the surface manually with a net once a week.

Plant aquatic plants like lily pads and water hyacinth, especially in areas where your pond is less than 2 feet deep. These plants shade the bottom and slow algae growth by depriving it of light. Shallow parts of a pond are most likely to harbor pond moss.

Make sure you don't have too many fish in your pond. A pond can support 6 inches of fish per 100 gallons of water. Also take care not to overfeed your fish. Nutrients from fish food and fish waste feed pond moss and help it grow.

Prevent water runoff from your yard into the pond. Organic material from the yard feeds the algae. Chemicals from fertilizers, herbicides and pesticides kill bacteria that feed on the algae and disrupt the microbial balance in the pond.


Do not attempt to kill pond moss all at once with a chemical algae killer. Although it is quite effective in the short-term, it will cause even worse future algae blooms. The dead algae sinks to the bottom and feeds new algae, and the increased sunlight to the bottom helps them grow.

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