When it comes to pond filtration there are many different kinds being used today. However, they all fit under one or both of two types. The two types are biological and mechanical filtration. Biological filtration is designed to grow the necessary bacteria for keeping a pond healthy. Mechanical filtration is used to remove debris, and nutrients from the pond manually. Both types are necessary for achieving a healthy, balanced, and clean pond. But no matter how sophisticated these filters become they will never be able to accomplish what nature is able to do so efficiently.