Fertilizing a pond may increase the productivity of the pond by as much as 400%. When fertilizing, the goal is to produce an "algae bloom", which usually turns the water a green color. This algae bloom is actually billions of microscopic algae cells that act as the base of the food chain in your pond. By increasing the amount of food in the base of the food chain, you will increase the amount of food available to all sizes of fish.
Begin fertilizing when the water temperature approaches 60 degrees (normally in late February or early March in the southern U.S.). Make the first application at twice the recommended rate, to stimulate the bloom. After the first application, fertilize once every two weeks at the normal recommended rate until the bloom becomes established. Once the bloom is established, you will fertilize as needed based on the water visibility.