Boosting the Bio capacity of your pond will increase its ability to keep itself clean.
This can be done by:
Adding a bio filter: Click the Biofilters link above
Increasing the amount of surface area for beneficial bacteria growth in the bio filter (See Filter Media)
Increasing the surface area for bacteria growth outside the bio filter by adding floating plants and potted plants in floating islands (See floating planter islands)
Adding cultured bacteria that are free floating such as Microbelift PL (See Microbe-lift Bacterial and Enzyme Products)
Increasing the amount of oxygen in the water to allow more aerobic bacteria to thrive (See Pumps and Small Aerators)