If the pond pump could be considered the engine room of the water maintenance system, then the pond filter could be described as the cylinders and the bacteria as the petrol. Basically, the pump and the filter are mechanical components of the system but the actual energy for the cleaning comes from an entirely natural entity, just like the petrol in an engine.

The pond filter is performing two functions, firstly the filter will have a system such as sponges that are designed to sieve the water for physical particles. As the filter requires the pond water to be pumped through it, there will inevitably be quantities of physical debris being continually fed into the filter. If allowed to collect on the surface of the biological element of the filter. It would work less effectively.

Having initially removed some of the physical debris, the real specialist work of the biological filter takes place. The key part of the filter is the bacterial media. This is an environment specifically designed to host the bacteria that effectively clean the pond water.

The bacteria perform the all important function of turning ammonia, which is produced by fish, firstly into nitrates and then into nitrates. These nitrates latterly go on to be the primary food source for the plants in the pond. It is the plants that then produce the oxygen that is ultimately required by all of the organisms in the pond.