The key to establishing a healthy pond is selecting the correct filter. Filtration happens in two forms, mechanical and biological. Mechanical filtration traps suspended matter (uneaten food, fish waste, dead plant matter etc) pumped from the pond. Biological filtration cultures beneficial bacteria that digest liquid waste (from fish, and decomposing food and vegetable matter), breaking it down into a less harmful form. A good filter system will provide both mechanical and biological filtration. Due to their size most mechanical and biological filters are mounted outside the pond and a submersible pump is used to pump the water from the bottom of the pond into the filter where it passes through the filter media before being returned to the pond.
