Pond filters perform the same three functions as aquarium filters. They trap solid debris (mechanical filtration), they remove dissolved impurities (chemical filtration) and they break down fish waste using heterotrophic bacteria (biological filtration). Simply put, determining what type of filter to use on a given pond is a function of size, the amount of leaves and other solid material that will fall into the pond, and bio-load (the number and size of fish and the feeding regimen).
The simplest form of pond filter is the internal or submersible filter, which, as its name suggests, sits on the bottom of the pond. A pump is attached that draws water through media in the filter box and discharges it either underwater, up a fountain stem or through a hose to the top of a waterfall or spillway.
Danner Manufacturing’s Pondmaster series of time-tested and versatile internal filters come with two fibrous pads: one that acts as a mechanical/biological media, and a carbon-impregnated fine-mesh pad that traps fine particles and chemically filters the water. They have a low profile and are black in color, making them easy to conceal. Hagen’s Laguna PowerFlo Max Filters offer modular chambers that can be loaded with different media and attached in sequence to meet the owner’s filtration needs.
Internal filters are relatively inexpensive and are designed for smaller ponds. Their main drawback is in retrieving them for cleaning. The hobbyist has to enter or reach into the pond, being careful not to let dirt and debris spill back into the water.
Pressurized canister filters offer pond owners several advantages over internals. They are designed for medium-sized ponds – or small ponds with larger bio-loads – and are installed next to the pond, making them easier to access for cleaning. They can be partially sunk in the ground to help conceal them, or, if used with a more powerful pump, they can be placed in a remote location such as a garden shed.
A submersible pump sends water to the filter, and a discharge hose is run from the filter back to the main pond or to the top of a waterfall or spillway.
Pressure filters typically come with mechanical and biological media, but can accommodate chemical media, such as carbon, if placed in mesh bags. Many canister filters, such as Tetra’s Bio-Active Pond Pressure Filters and Laguna’s Pressure-Flo Clean Filters have backflush valves that allow longer intervals in between cleanings. They are also available with integrated UV sterilizers that eliminate green-water algae blooms and kill disease organisms.
For larger ponds, a skimmer box and waterfall filter combination works best. The skimmer box is sunk in the ground and the liner is attached to an opening that draws water in. Leaves and debris are trapped in the skimmer, and a high-velocity submersible or in-line pump sends the water to a multistage filter box at the opposite end of the pond. The main filter box can be positioned at the pond edge or the top of a waterfall or stream and concealed with rockwork or other decorative material.
Laguna PowerFlo High Efficiency Water Fall Filtration System offers removable media baskets that allow the pond owner to choose a variety of media and make it easy to clean. The Laguna Skimmer has a lift-out debris net for fast and easy maintenance and the weir door regulates water intake to the pump.
Helping the Purchase
When deciding what type and size filter to purchase, pond owners should consider pond size, numbers and size of fish to be stocked, the amount they will be feeding their fish, and how much debris in the form of leaves, twigs and other material might fall into the water. Most manufacturers put a recommended pond size in gallons on their filters, but this does not take into consideration the biological and dirt load the pond will carry.
To be on the safe side, always recommend a filter that is 50 to 100 percent larger than the pond it will be used on. Remember, fish grow and multiply, and owners don’t always have control over how much organic material will make its way into the pond. Choosing an oversized filter is always a good idea.
If possible, have working examples of the filters being sold for shoppers to observe in action. If a pond or water feature in possible in the store, retailers have dry demos out for customers to experience close up. Remember, aside from the liner, a pond filter is the single most important item customers will buy.