These filter cartridges are for the Aquatop hang of the back filter line. (Note: The Forza 5 - 15 is also known as the PFE-1)
Aquatop recommends replacing the filter cartridges every 4 to 6 weeks. Aquariums with heavier stock should be replace their cartridges more often.
Rivers to Reef says: If you are trying to be frugal, you can give these guys a rinse before replacing them, but keep in mind your carbon is going to be exhausted, so all you will be doing will be buying some time for your mechanical filtration. Rinsing also buys just a week or two at most, it will not buy you another month. We really do not recommend rinsing more than once because the filter media will begin to break down and can make a mess of things.