Pond filters range in style, size and function. Often multiple styles are used in one application. Size would be determined by gallons of water, fish load and exposure to elements.
Pond skimmers are your first line of defense to prevent debris (leaves) that have fallen into the pond, from dropping to the bottom. A skimmer draws the surface water into a basket or net to keep surface water clear.
A pressurized filter cuts down on much of the manual cleaning of the pond. A solids handling pump at the bottom of the pond feeds the bottom water (sludge and debris) into the pressurized pond filter. The pressurized filter has a backwash system that will flush out the debris when you choose. The filter media within the pressure filter holds on to beneficial bacteria as well as traps unwanted debris that will later be backwashed out. A UV system is often incorporated into a pressurized filter to keep the water clear of suspended algae (green water).
As mentioned above a UV sterilizer or UV clarifier utilizes a UV bulb which kills the microorganisms (algae, bacteria) that are able to flow through the unit. UV clarifier/sterilizers are most often used to keep pond water clear. They can be used as a separate filter unit or they can be integrated into a pressure pond filter or bio filter unit.
UP FLOW FILTER
An up flow pond filter is fed by a pump from within the pond. The intake on the filter is at the bottom of the unit. The water will pass through the layers of filter media and cascade or spill from the upper lip of the unit – providing not only additional filtration, but a beautiful spillway for your pond.
An pond ionizer releases ions into the water through a probe which is placed in the pipe line, in the skimmer or in a stream. An ionizer is the only mechanism that can control/eliminate string algae that forms on the rocks, waterfall and edges of the pond.