Depends on how dirty it gets. with my aquaclear 300, I rinse out the sponge once or twice a month, I have had the same sponge for over a year. Biomax u can rinse out once a month up to 3-4 months depending on how dirty it is. Biomax should be replaced after 6 months in case the tiny pores are clogged with crap. I really never scrub out the entire filter... maybe once or twice a year i'll give it a rinse. I dnt have hard water so I dnt get much sediment. At this time I also take out the plastic propeller and rinse it off/ detangle it. Carbon should be replaced once a month or sooner if you use it. The ammonia resin insert can stay in for over a month if you use that.