Pump fed filter systems are the most common filtration setup for ponds of all sizes. A pump, usually submerged in the pond, pushes water along a length of hose through a UVC and to an external filter, where the water is processed before it returns to the pond.The component sequence is;

Pond ? Pump ? UVC ? Filter ? Pond

This system is relatively cheap and fairly easy to set up, and can be installed by the average water-gardener.Pump fed systems are limited as to the size of particles they can filter by the pump’s casing.

Box Filters

Box filters, or Flow-Through Filters, sit outside the pond, above the level of the water and receive water from the pump. Most modern box filters have UVCs built into the lid section. After the water has passed through the UVC it flows through the box’s filter media, through the outlet and returns to the pond under gravity.

Box filters can be adapted to contain almost any type of filter media, and because they come in a wide range of sizes, they are available for ponds of massively varying volumes and stock densities.Because they empty under gravity, box filters need to be situated close to the pond’s return, i.e. at the side of the pond or top of a waterfall.It is not advised to add extended lengths of pipework to the filter's outlet, as any restriction on the flow exiting the filter may cause the water to back-up, and could flood the unit. Maintenance is carried out by removing the lid, and removing and manually cleaning the filter media. Most box filters have been manufactured to contain a large amount of surface area, so routine maintenance is reduced.

Pressurised Filters

As with box filters, pressurised filters are situated outside the pond and are fed water from a pump via a length of hose, they also have built in UVCs.

The biggest difference between box filters and pressurised is that pressurised filters are enclosed units, so the water leaves the filter under pressure from the pump. A hose is attached to the filter’s outlet to return the water to the pond, so the filter can be installed away from the edge of the pond and it can be buried up to the hose tails. The biggest benefit of this, is that there is no unsightly filter box at the side of the pond to try and hide, leaving the garden looking tidier and the pond area more natural.Most pressurised filters have a back-flush system which, when engaged, reverses the flow of water through the filter. This unblocks the media, and sends the water out of a waste outlet.You don’t have to remove the media and get your hands dirty every time the filter needs cleaning. You simply attach a length of hose to a waste outlet, switch to back flush, and let the dirty water run to your flower bed to fertilize the plants, compost heap, or simply down a drain. When the water runs clean, switch the flow to return to the pond.Pressurised filters tend to be more expensive than box filters with a similar capacity, and because they are more compact, they have less surface area and require more regular maintenance.