A filter will need checking from time to time to make sure algae is not clogging it up. Apart from that, it should normally be kept running 24 hours a day. You should normally clean 25% of the foams in your filter once every 2-4 weeks in pond water, as long as it is sized correctly and the pond is not overstocked with fish. However, you should only clean the foams when absolutely necessary (usually when they have become completely blocked). The plastic media should not be cleaned, as this would risk killing essential bacteria. A normal cleaning regime, as we have just outlined, would mean that you would need to change the foams after approximately 3-4 years.