Too many fish can cause problems in your water garden. A general rule of thumb for most water gardens is 1 inch of fish for every ten gallons of pond water. A five hundred gallon water garden should contain a maximum of fifty inches of fish, or five ten-inch fish.
Keep in mind that fish grow throughout their entire life and fish, especially goldfish, reproduce. Always stock your water garden to match your fish’s expected maximum size. Koi routinely reach 26-30 inches while most goldfish will reach 14 inches.
Overstocked ponds will result in poor water quality and clarity. Fish disease and algae in the garden pond will become major issues if action is not taken in a timely manner.
Increasing the size of the pond filter may tempora.