Biological (External Box) Pond Filters

External Biological box filters, as the name suggests, sit outside the pond & process the water that is pumped to them from a pond pump submersed in the pond water. Through a process of mechanical filtration particulate material is trapped & can then be removed. Biological filtration utilises aerobic bacteria to break down the most toxic products of fish waste & organic decay & together the two processes clean & purify the pond water. A filter is a useful component for most ponds & absolutely essential for ponds containing fish. 

inclusion of an Ultra-Violet Steriliser will guarantee that the water will not go green as it will kill off the green water causing algae. An added benefit is that the U.V. component may also help reduce the background levels of pathogens that can effect the fish, especially harmful bacteria & fungal spores.

Box Filters must be situated above the maximum water level.
See also "Pressure Filters", "Submersible (in-pond) Filters" and "Floating Filters".