Wow what a revolutionary idea! Unlike the sponges in all of the pond filters that have gone before it, the Bioforce Revolution employs a mechanical filter consisting of many little square foam blocks. When in position with the pump running as usual these filters join together to create an effective filter barrier. Switch off your pond pump and turn the cleaning handle on your filter - the solid ring of foam breaks down into individual pieces that bang together and dislodge dirt. Switch on your pump, direct the water to the waste outlet and watch in amazement as the dirty water goes to your drain. After 20 seconds or so (or until water runs clear) switch the water direction back to your pond. So simple....sure to be a winning idea! Quote \"REV\" in shopping basket for free delivery.