Goldfish add life, color and movement to a garden pond. Common goldfish are an inexpensive addition to a pond and they can contribute to pond health by eating mosquito larvae and algae. Be careful not to crowd the fish. A good rule of thumb is to add no more than six 3- to 4-inch fish to a pond that contains less than 500 gallons of water and five or six 5 to 6-inch fish to a larger pond. Another rule says to allow one inch of fish for every 8 gallons of water. If you add too many fish your pond's biological filter won't be able to keep up with their waste production and the pond water will be fouled and the fish could die.
Purchase only healthy fish from a reputable dealer. If you buy pet-store fish, make sure they have no sores, missing fins or sluggish behavior.
Float the bag your new fish are in on top of the pond for 15 minutes. This allows the temperature of the water in the bag to gradually equalize with the temperature in the pond.
Open the bag and continue to let it float in the pond. Some of the pond water will mix with the water in the bag.
Submerge the bag completely after another 15 minutes and allow the fish to swim out into the pond.