The filter in your aquarium will require regular maintenance to keep it running effectively and to prevent any breakdowns. A well maintained filter will last years longer than a poorly maintained one.
How often does filter media need maintenance?The sponge(s) within the filter will need to be periodically cleaned to prevent them from clogging and reducing the water flow. A slightly dirty sponge however, is more effective than a brand new, or clean sponge.
The bacteria that convert toxic pollutants into less harmful chemicals will thrive in dirty conditions. However, if the sponge becomes to dirty, the flow rate will slow down and other, less useful bacteria will grow. This results in a drop in oxygen levels and the useful bacteria may suffer.
Internal filters, which generally have smaller sponges and less powerful pumps, will need to be cleaned at least fortnightly. External filters however, have larger sponges and more powerful pumps, so are less likely to clog as quickly. External filters under normal aquarium conditions need only be cleaned every 3-4 weeks.
There are of course, other types of filter media than sponges, particularly for external filters. Carbon or carbon sponges (Normally black sponges) should be replaced at least every 2-3 months, after this time, they may begin to release chemicals that have previously been removed by the media.
Filter-floss medias (cotton-wool like sponges) should be replaced every week if possible, but this does depend on the individual aquarium conditions.
Biological media, which is normally in the form of ceramic or sintered glass (which confusingly, does not look at all like glass) nodules, should be cleaned every month. Biological media should only be lightly rinsed however, not thoroughly cleaned.