An algae bloom can quickly cover your pond and take over. When the algae dies, the process of decomposition uses much-needed oxygen in the pond, which can kill your pond fish. Unfortunately, chemical treatments for algae can also harm the plants and fish in your pond. Prevention is the best algae treatment in ponds, but you can also use some non-chemical methods to reduce algae that has already grown.
Construct your pond where it will not catch rainwater runoff from the yard. If your pond is already established, construct a barrier to keep rainwater out; yard runoff contains organic materials which provide nutrients for algae growth.
Install a pump and filter; the pump should be big enough to move half of the pond's volume every hour.
Install a pond skimmer; this device will remove most debris before it reaches the bottom and starts decaying; this decaying matter provides algae with nutrients.
Vacuum or siphon your pond's floor regularly to prevent buildup of decaying matter.
Add enough floating plants to your pond to cover 50 to 75 percent of the water's surface. This will limit the amount of sunlight in the pond and prevent algae growth.
Include a good balance of other pond plants, as well; these plants will compete with the algae for nutrients and starve it out.
Add a bio-filter with nitrifying bacteria to your pond; these will also use the same nutrients as the algae and help starve it out.
Apply chemical algicides as a last resort, and use caution to prevent harming the other pond plants and fish.