Remember, marineland has a vested interest in your support of carbon use. Carbon does have its place, but it doesn't really remain effective for 2-3 weeks or a month. 2-3 weeks may be more accurate if you purchase high quality
GAC, but the stuff that comes prepackages is usually crap. Even most medication inserts will tell you not to bother with removing carbon from filter if its more than a week old.
I personally do not use carbon, I don't need it. Carbon has ties with HITH, and since I originally wanted Oscars, I didn't want to risk it.
Carbon DOES provide lots of biofiltration surface area though.
As mentioned above, when changing the filter media, cut out a portion of the "wooly" part and stick it behind the new filter to "seed" it for a week. I'm on the same filter pads (just washed) for about 8 months now. So you don't NEED to change them that often. When you rinse, and replace - and the water flows over the intake tube anyhow...that's when its time for a new cartridge.
think about considering a new filter, with a biowheel (mini). Then, the filter pad change will be a moot point!