I clean the filter media only when it is clogged with debris, and then, as has been posted, with spent tank water. I disagree about the carbon, as I do not use it at all unless I need to remove a medication from my tank. Also, be careful not to clean out your filter at the same time that you do other significant cleaning, as this disrupts the biofilter. I try to clean my filter on days when I have not done a gravel vac for this reason, though that might be more cautious than is necessary.