Active carbon filters at a glance replaceable active carbon filter gets rid of unpleasant smells and keeps the water fresh for longer coarse foam filter keeps the water clear of hairs and other impurities can be cleaned under running water inspect the active carbon filter every 2 4 weeks if your pet uses the water fountain the filter should be changed every 30 days depending on the frequency of use if multiple animals use the same water fountain you should change the filter more often