The pump must be capable of taking up a certain amount of solid material if it is required to function with a biological filter

This easily dismantled Blagdon Hydratech pump qualifies extremely well as a filter pump. Not only is it capable of pumping water containing 5mm solids, if there is a blockage in the impellor it automatically reverses until the blockage is ejected. It sounds mad but it works.

The pump must be capable of taking up a certain amount of solid material if it is required to function with a biological filter. A dense sponge pre-filter on the inlet is out of the question. As for performance, a pump and a filter must be able to process the total volume of the pool in two hours. Therefore in a pool of 1000 gallons or 4500 litres, the pump should be capable of delivering to the filter 500 gallons or 2250 litres at the height above the pool surface that it happens to be set at.

Most manufacturers are at pains to point out that the figures they provide only hold if the maximum bore pipe-work that it is feasible to use is used and that fittings are kept down to a minimum. Back-pressure from constricting fittings can also affect the longevity of the pump, particularly on the more old fashioned designs. Just the length of hose itself can reduce the performance of some pump designs quite radically. Estimate to lose between 60 and 100 gallons per hour for every 10foot length of hose (in litres per hour, between 273 and 455litres) even on the horizontal.