I usually rinse out my filter pads/cartridges in the dirty tank water every 2nd water change (I do weekly water changes). Around every 4-6 weeks I float the pads/cartridges in the tank and fully clean the filter itself. I only change the cartridges/pads when they won't come reasonbly clean, about every 6 months or so (I don't use carbon, those need to be changed every 4-6 weeks). I run 2 filters on my tanks, so I stagger when I change cartridges as not to remove all the bacteria at once.