How big should a pond filter be?
The old maxim for biological filter size is usually stated as ‘the filter must be equivalent to 25 to 30% of the surface area of the pond . This statement makes absolutely no sense until you apply it to a gravel bed filter installed in the pond itself. Well you can still use the ‘in pond gravel bed filter but maintenance and cleaning can be difficult and awkward. Today we supply a range of pond filtering options, for the removal of ammonia, nitrite and suspended solids which are easier to install manage and maintain.
The biological media used today is very different to ordinary gravel and pea shingle.
Remember, waste is produced by fish, not pond water, so 10 kilos of fish in 5000 gallons will not need the same amount of filtration as 50 kilos of fish in 5000 gallons. All biological filtration media provide a surface area for colonisation by nitrifying bacteria. Some have greater surface area per volume than others, and some have other characteristics which filter heavy or fine suspended solids more efficiently than others. This is dealt with in more detail in the media section.
The work carried out at various universities in Europe and America to establish the ratio of live fish to media means the size of a filter can more easily be derived. The minimum media required to remove ammonia can be provided in this general rule.
1Kg of fish fed at 1.5% of body weight per day with 36% protein feed will require 0.8 M2 of surface area of biological media. For example, Flocor RS has a surface area of 230 M2/M3 (or 1000L). To filter the ammonia and nitrite as produced by 1Kg of fish, then 3.5L media would be required. This amount refers to submerged media, in trickle filters the amount required is less.
