Working in conjunction with proper pond design, one must choose the optimum filter for the best possible result. These include Trickle Towers, Bead Filters, Bog Filters, Vortexes, Skimmers, Bottom Drains, and Aeration. There are two forms of filtration, Mechanical & Biological. Mechanical filtration is simple; it is the removal or trapping of solid particles (detritus) in the water. Biological is the promotion of nitrifying bacteria which is explained in “Pond Design”. One does not always go hand in hand with the other. An advanced aquatic specialist will have both these aspects mastered.
My personal favorite. The trickle tower or the wet/dry filter is a filter that exists above the water level and is pump fed from the pond. The pump can only be placed before the filter and water flow back to the pond via gravity. The filter works on the principle where water is “showering” or “trickling” over filter media. This will create the greatest amount of beneficial bacteria because of the high levels of oxygen.
Bead Filters are filters that exist above or below the water level of the pond. They are excellent for mechanical and biological filtration. With the aid of an air blower agitator the bead filter backwashes with ease.
Bog Filters are vegetative filters or aquatic plant filters that exist in the header pool that makes up space behind a waterfall. Water is pumped into the bottom of the header pool that is filled with filter matting and then moves over the spillway of the waterfall back into the pond. Marginal plants such as Iris, Sweet Flag, and Water Sedges are planted directly bare root into the matting. Beneficial bacteria will grow in the filter matting, making this an effective natural filter. Bog filters can be used alone in a small garden pond but additional filtration is needed for Koi ponds. Here is an example of washable plant media with healthy plants growing in it.
The Vortex Filter is a cylindrical container that is set level and adjacent to the pond connected via a bottom drain. This is a gravity-fed system where water enters the drain and is pulled through the vortex by an external pump or a submersible pump. This water is spun around where sediment and solids fall to the bottom of the vortex and then can be eliminated through a purge valve. The vortex is not a biological filter but a mechanical one.
Skimmers – Bottom Drains:
Pond skimmers and bottom drains are similar to those in an in-ground pool. Pond skimmers are excellent for eliminating debris that enters the pond by its surface. The pond skimmer is an excellent area for automatic fill values and overflow ports. Skimmers can be used as the sole method for moving water from a water garden only, a monthly vacuuming is necessary to remove solids from a gravel free bottom. A skimmer used in conjunction with a bottom drain or submersible pump is ideal.
Bottom Drains are outstanding and are recommended in every Koi pond. They are 100% effective in removing all solids off the bottom. Solid handling submersible pumps can be used in place of a bottom drain although they are not as ideal (see Proper Method for more details).
Dissolved oxygen is crucial in a pond with fish and is necessary for nitrifying bacteria to exist and thrive. Aerators are external to the pond and bring air to the pond through air stones or an air diffuser that is located on the top of the bottom drain. You must have aeration any in a pond with fish.