Resource icon


All Water Features support life. We know that any surface that remains wet with water will support, at the least, a microscopic biofilm composed of bacteria, archaea and algae. In decorative water features such as formal fountains, water walls and rock bubblers, because of aesthetic considerations, the water is usually treated with chemicals to inhibit the growth of this biofilm.

The opposite is true in Water features that are purposely constructed to support life such as a Water Garden, turtle pond, Garden Pond, etc. This biofilm growth is desired and , indeed, encouraged for it is the foundation of life. It supplies the basic mechanisms in the Nitrogen cycle as well as the Carbon cycle. The greater the surface area of this Biofilm, the more varied and the larger the organisms that can be supported. Only when this surface area is large enough can a stable population of fish be sustained and thrive. There must be enough biofilm to oxidize the ammonia and other wastes produced by the fish and support an adequate food chain.

In nature, this balance is a naturally occurring process. It is when we strive to construct artificial aquatic environments thatsome outside intervention is usually required by providing supplemental bio-conversion through the use of ‘biological filters’ and by supplemental feeding that may be needed to correct any existing food chain deficiency.

These questions arise:

Do I need ‘bio-filtration’?

If the water feature is strictly a water garden (no fish, turtles, ducks etc), supplemental bio-conversion is not needed. However, if the water feature is to house any of these, then additional bio-conversion is usually a definite requirement. Granted, although a feature of large enough submerged surface area may comfortably support a limited fish population, most people neither have the space or desire to dedicate a few thousand square feet of property to house a handful of fish.

What type and size of ‘bio filter’ do I need?

Type of ‘bio-filter’ is a matter of personal preference…cost, ease of maintenance and possibly aesthetics are possible considerations. Size is of greater importance only as it relates to filter media capacity which itself is dependant on the type of filter media used, the quantity of said media being dependant on its Specific Surface Area (SSA) and primarily on the fish load (biomass) in the Water Feature. (Additional information on SSA and fish load can be found on the internet with a simple web search.)

This brings us to the real purpose of this article; the fact that, in most instances, manufacturers of bio-filtration units supply incomplete and often misleading information on actual filter performance. Some only give the maximum flow rate, many rate their filter on total gallons of pond capacity (Is that without fish? If it is with fish, how many?), still others classify their filters pond capacity with sub classifications of ‘No fish, a few fish, or a heavy fish load”

How many are a “few” and what constitutes “a heavy fish load”. Some give the maximum number of fish in total inches of length which can be dangerously misleading (a 10” fish has considerably more biomass and produces proportionately more waste than two 5” fish of the same specie). One manufacturer does correctly state that it depends on the type of filter media used. Only one manufacturer, that also supplies the media with their filters, gives an actual maximum fish load (in pounds). A koi length/weight calculator is available at

Is it surprising then that because of this negligence on the part of the manufacturers new pond owners quickly begin to have problems maintaining water quality? Could this all be due to the fact that they were given incomplete information on the performance abilities of the biological filter they purchased?

Is it truly negligence on the part of the manufacturers? Or carelessness? Or incorrect prioritizing of published technical information? Or is this crucial information withheld knowing that subsequent problems may arise forcing the consumer to purchase yet another piece of equipment or an otherwise avoidable chemical treatment?

It is time that the water feature equipment and supply manufacturers adopt industry wide standards concerning labeling and product performance information that would be truly beneficial to the consumer. Knowingly withholding any vital product information seems, at the least, unethical and unprofessional. Some may even feel, and understandably so, that it borders on the criminal.

Before you purchase any filtration unit, ask the important questions and insist on detailed and specific answers. The health and longevity of your fish depend on it.