Pond Boss Forums AQUATIC VEGETATION Controlling unwanted plants Algae problems: Aeration, chemicals or both?

Tree leaves and nutrient recycling are the likely sources of increased phosphorus stimulating algae growth.
Phosphorus testing can be deceiving. Phosphorus measured as total P includes all the phosphorus in all the organic material of the sample including the algae. So when algae is abundant total P is usually abundant due to all the P in the algae. IMO the proper P measurement is ortho P (aka dissolved P or soluable P) which is the available phosphorus that is being used or available to the algae for more growth. Both types of phosphorus can reflect the trophic conditions, each providing different information.

Alum treatments do reduce the phosphorus in the water column and precipitated alum forms a layer on the sediment helping to seal the top layer on the sediment slowing the release of P from decay. Note this works best in deeper waters and is temporary. As phosphorus laden inputs persist P increases and the problem resurfaces or reoccurs. Often the best long term approach for an old hypereutrophic pond is rebuilding. Rebuilding should be done so phosphorus inputs are minimized. To reduce expense of pond rebuilding, the pond can be down sized. Large ponds cost more to maintain when anything has to be done. It is the rule. Bigger is not always better.

Whenever you get the algae under control aeration and algaecides are some of the tools in the pond management tool box. Aeration by itself can only do just so much for improving a pond. In big problem situations other tools are needed.