How to Kill Pond Moss

Pond moss and algae can pose a significant risk to the health of your water garden or farm pond. Not only does the moss and algae use up your pond's oxygen and dissolved nutrients, but they may also choke out the ornamental plants you wish to grow. Pond moss can quickly propagate and take over the bottom and edges of your pond. Take immediate steps to kill the moss to resolve the problem and maintain a healthy, balanced pond life system.

Obtain potassium permanganate to kill the moss. This option is best for those with light to moderate moss growth. Potassium permanganate is available at most pond supply stores and some animal feed stores. When used properly, the product will not kill your fish or nearby waterfowl.

Calculate the acre-feet of your pond by multiplying the pond's surface acres by its average depth. For example, if your pond covers half an acre and has an average depth of five feet, its acre-feet is 2.5.

Multiply the pond's acre-feet from step two by 5.4. The result is how many pounds of potassium permanganate you need to use to achieve a concentration of two parts per million. This concentration will kill most algae and moss. As an added perk, it will also kill most viruses and bacteria present on your pond's fish or in the water. Add the appropriate amount of potassium permanganate to your pond. Sprinkle into the water while walking along the edge of the pond.

Use an aquatic herbicide as an alternative to potassium permanganate. This option is best for those with heavy moss growth. For best results, choose a product formulated with copper-ethylenediamine, which will not harm fish. Example products include PBI's PondMaster Herbicide. Apply according to the specific product's guidelines for the acre-feet of your pond, as potency varies according to the herbicide.

Prevent the moss from growing back. Moss and algae typically appear due to a nutritional imbalance in the water. Make sure there is no water runoff entering your pond, a common source of excess nutrients that may feed moss. Reduce the amount of sunshine in the pond by adding a pond dye such as AquaShade, which retards algae and moss growth. Consider adding pond plants such as lilies to use up excess nutrients in the water and shade the pool bottom where moss may grow.

Things You Will Need

  • Potassium permanganate
  • Pond herbicide
  • Pond dye
  • Pond plants


  • If your pond is large, you may need to use a boat to equally distribute the potassium permanganate or aquatic herbicide.


  • Potassium permanganate is expensive and typically costs an average of $80 for a standard five-pound package.

About the Author

Joshua Duvauchelle is a certified personal trainer and health journalist, relationships expert and gardening specialist. His articles and advice have appeared in dozens of magazines, including exercise workouts in Shape, relationship guides for Alive and lifestyle tips for Lifehacker. In his spare time, he enjoys yoga and urban patio gardening.