It is typically recommended to do a 50%+ weekly water change to keep water parameters in check & to replenish minerals. As for the filter media, rinse it in USED tank water weekly or every other week, replace it only if it is falling apart. Personally I quit using filter cartridges because they seemed to either fall apart or clog quickly, I now only use sponge in my HOB
filters which last much longer & are easily rinsed when I do a water changes.
EDIT: ammonia/nitrItes should be 0, nitrAtes <20