Limit your fish load. A good rule of thumb is 1 inch of fish for every 10 gallons of pond water. Keep in mind that fish grow and reproduce. Take in account the fish’s maximum size when stocking your pond.
Don’t overfeed the fish. Feed only what they’ll eat in a few minutes. Remove any uneaten food from the pond water.
Maintain your pond filter. Sludge on the filter media in the filter can suffocate beneficial bacteria causing the filter to crash.
Test your water quality regularly. Normal testing should include pH, ammonia and nitrite. The water quality in small ponds can change quickly.
Do water changes. Change 10% of the pond volume weekly or 20% every two weeks. Remember to dechlorinate your water if you are using a municipal water source