What you have there is referred to as a 3 stage filter, mechanical, biological and chemial. The mechanical element is the gauzy type pad it filters out particulate matter, the biological is the one with all the stubby fingers where benifical bacteria is supposed to colonize the chemical is the one with the activated carbon. The carbon will only be effective for about two weeks, you will have to wash the mechanical element as it become plugged you will know this by the amount of bypass you are getting, the biological should never have to be replaced you might need to remove excessive growth from time to time but the less you fool with it the better. Do a web search anyone producing such a filter wants to do repeat business in replacment media. If you have a properly stocked tank and are doing frequent water changes the carbon element is not necessary. It looks like a pretty good filter to me. Scott try clearseal.com