Pond Algae Control
Once you have a problem with pond algae, there are a couple of options for controlling the situation. The most common is to add a copper based algaecide, either in dry or liquid form, to kill the visible algae. You want to avoid not killing too much algae at one time because it will take most of the available oxygen out of the water and you may end up with a fish kill. Most companies recommend treating one-third of your pond at a time. Algaecides can be effective at controlling what you can see, but this does not address the bigger problem. As a result the algae problem will come back time and again. Killing the algae can also contribute to more and more excess organic matter as when it dies. It will sink to the bottom, adding yet another layer of rich, black organic matter that feeds more algae.
Grass carp sometimes eat algae, but it is not common. They have been seen eating plants coated with algae, but their mouth and gills are not positioned to eat algae effectively. Although grass carp can be used to control some aquatic weeds, they should not be stocked to control algae. In fact, grass carp can add to a nutrient problem and cause algae to multiply if they are no longer eating aquatic weeds efficiently.
The existence of algae in you pond may be a fact of life, but it is good to know that there are ways to prevent excessive growth of it and there are ways to control it with some patience and the right tools.