How to Get Rid of Seaweed in a Pond

Install a pump. The ideal pump should move at least half to the entire volume of your pond per hour. To calculate your pond's water volume, multiply its length, width, and depth by a factor 6.7, 5.9 or 7.5 for oval, circular, or rectangular ponds, respectively. Alternatively, use a pond water calculator or speak to a home and garden professional.

Consider adding an additional aeration device, such as a waterfall, fountain or aerator. Keeping the water moving makes seaweed less likely to grow.

Add aquatic plant life. Underwater plants such as anacharis will absorb nutrients that would otherwise go toward seaweed growth. Floating plants such as water lilies, water lettuce or water hyacinth provide shade, limiting the sunlight that seaweed needs to grow.

Skim the surface of your pond with a skimmer net or seaweed rake to manually remove seaweed. Both should be available from your pond supplier.

Consider adding seaweed-eating fish such as grass carp to your pond. These will help limit the nutrients available for seaweed growth. If you already have fish and don't wish to add any more, limit the amount of food you give them daily.

Control water runoff from other areas of your yard. Rain and other water runoff can carry organic material and fertilizers into your pond, promoting seaweed growth. If your pond receives a lot of runoff, plant vegetation around it to buffer the water flow.

Filter or sterilize the water. If you already have a filter, replace the media often and use activated carbon to remove additional nutrients from the pond. Additionally, you can install a UV sterilizer.

Add blue or black dye to your pond to limit the amount of sunlight penetrating the water. Dye is often cheaper than herbicides, but some brands should not be added to ponds that contain fish.

For more aggressive algae control, try herbicides such as copper sulfate, diquat dibromide, barley straw or the commercially marketed AlgaeFix. Pond chemicals often need to be added over a period of time. For best results, consult a home improvement specialist who knows about ponds.