Pond Filter pumps have to be able to pump high volumes of dirty water continually to a pond filter system. The pumps impellers need to cope with large amounts of solid matter without becoming blocked. This type of design makes filter pumps more expensive than the traditional type of fountain pump. The filter pump is normally housed in a casing that has holes or a grid system to prevent fish or other pond life from being sucked into the impeller.
What Size Filter Pump?
This depends on the type of pond you have, Ponds can roughly be divided into two categories, Garden Ponds and Koi Ponds. Garden Ponds are normally planted with marginal, oxygenating plants and water lilies and house small fish like goldfish orfe and shubunkins. For this type of pond you will need to turn over the ponds water volume approximately once every two to four hours. So for example, a garden pond of 1000 litres capacity will require a pump that outputs between 250 - 500 litres per hour through the filter.
Koi ponds need more water turnover. These fish are normally kept in bare ponds without plants which they invariably eat. If you keep Koi you will need a filter pump that can turn over the ponds water volume once every one to two hours. So a Koi pond of 1000 litre capacity will require a pump that outputs 500 - 1000 litres per hour through the filter.
You also then need to consider the height of the filter above the ponds water level as the filter pump will need to pump the above output volumes at that height. You will need to study the pumping specifications on the box to establish the correct size pump for any given height.