Filter maintenance?

I think it really depends on stocking level, I have a ac 20 on my 6 gallon betta tank that I clean every other month.
 
Like said above simply swoosh the dirty media in tank water removed from a water change, to knock off some of the gunk. The frequency depends on how much you feed, what you keep, etc. If you are having trouble with algae you may want you feed less, or not leave your tank lights on as much. A general rule on feeding is to only feed an amount that can be consumed by your fish in 1-3 minutes. Feed a quality food like NLS, will allow you too feed less food which in turn will help your water quality. You can also consider buying a filter bag (.99 or so) and stuff it with polyfil, then put it in your HOB with your current filter medias, this will help polish your water.
 
AquariaCentral.com