I usually wash my filters in tank water every 2-3 weeks, i dont think it really needs to be replaced but once a year (1 of the 4 every 3 months or so). I wouldnt replace them though unless they get really gunked up and rinsing them in tank water doesnt seem to get them clean. My media baskets (4) have 3 baskets of bio media, and the top basket has filter floss, and that gets replaced/rinsed every 2-3 weeks as well.