How to Control String Algae


If a gardener's biggest problem in the garden is weeds, then a water gardener's biggest problem in the water garden is algae. Algae that grows together to form a long, hair-like filament is called string algae. String algae that forms in water gardens along the surface of the water. If a water garden is in balance, string algae is less likely to form. But once it forms, you can kill it with chemicals that will not harm your fish or aquatic plants.

Step 1

Attach a high-grade filter to your water pump. A high-grade filter will include a UV sterilizer light to kill bacteria and a carbon pad to remove wastes from the water as the water pump circulates it. String algae grow best in a bacteria-filled environment. By removing bacteria from the water, you can slow string algae growth.

Step 2

Add floating plants, such as water lettuce and water hyacinth, and place plants with roots in a basket filled with lava rocks instead of aquatic soil. Surface plants and rooted plants without soil will take their nutrients from the water. This will rob string algae of potential food in the form of nitrogen and phosphorous. Additionally, floating plants and those with large leaves shade the water. String algae will not grow well in shaded water.

Step 3

Remove dead leaves and vegetation from a pond to get rid of bacteria. When leaves and vegetation rot, they create a good environment for bacteria to grow, which can lead to algae.

Step 4

Include a heating device in your water to warm your pond so that it is above 60 degrees F, which is enough for tropical fish. Add the tropical fish to your pond. These fish will eat string algae.

Step 5

Add a natural bacterial control, such as AlgaeFix to your pond. Bacterial controls such as this are formulated to kill bacteria in a pond.

Things You'll Need

  • Filter with UV light and carbon filter pad
  • Floating plants
  • Lilies
  • Lotus
  • Plant baskets
  • Lava rock
  • Pond heater
  • Tropical fish
  • AlgaeFix bacterial control


  • Extension: Algae Control in Water Gardens
  • University of Kentucky: Use of Bluestone (Copper Sulfate) for Algae Control
  • University of Minnesota Extension: Container Water Gardening

Who Can Help

  • Ohio State University: Dyes and Aquatic Plant Management
Keywords: controlling string algae, cleaning garden ponds, killing pond bacteria

About this Author

Tracy S. Morris has been a freelance writer since 2000. She has published two novels and numerous online articles. Her work has appeared in national magazines and newspapers, including "Ferrets," "CatFancy," "Lexington Herald Leader" and "The Tulsa World."