Depending on the type of filter you have, it is generally recommended to clean the mechanical part, such as the skimmer or sponges, at least once a month. More may be needed if you’re in an area that has a lot of debris falling into the pond. If the type of biological filter you have includes pads, then they should be rinsed only once or twice a year. If the other media in the filter is of a plastic form, then it should never be rinsed unless it is clogged, and then it’s best if that can be done by using the pond water itself. This keeps the beneficial bacteria alive.