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.

Visibility can be measured using a white disk, 8-inches in diameter, attached to a rope or a stick. Simply lower the disk into the water until it disappears, then slowly pull it up until it reappears. Measure the length from the water surface to the disk. This is the visibility of the water. The recommended visibility range for an algae bloom is 18 to 24 inches. When the visibility is too clear (greater than 24 inches), it is time to fertilize. When it is less than 18 inches, the bloom is too thick, and you should not fertilize until the pond clears to 24 inches. When fertilizing based on visibility, you will fertilize about once a month. You should stop fertilizing around November when the water temperatures decline into the 50’s.

Note that your pond may not produce the proper algae bloom if the alkalinity of the water is low. Have a water sample checked and add agricultural lime if needed.

Never fertilize when undesired aquatic vegetation is present.
Fertilizer will stimulate its growth, creating a larger problem!