For that specific tank and filter it is OK to toss the cartridge if you want because it has the biowheel. The biowheel is never supposed to be cleaned or replaced unless it breaks. The bacteria will colonize the wheel so if you do toss the filter cartridge, you won't be tossing out the majority of the bacteria. I had that tank too but it got busted when I moved from alaska to NY in January
It's a different story if you are using most of the other filters. I have Aqueon and Tetra 10i filters and for those, I don't bother with their actual cartridges. I stuff the inside of the filter with Filter Sponge/foam made for the Aquaclear filters. This stuff:
If you do need the chemical filtration that you get from the carbon, that will become ineffective after about a month but unless you have smelly water or are trying to remove medication, chemical filtration isn't really needed. Sponge will last ALOT longer then the cartridges as well. I kept those till they started to fall apart anda then I started using the foam.
You might be able to stick some foam where the cartridge is supposed to go but if i remember correctly, it goes in the hood in a rather shallow location. I would think you could can easily cut a peice of aquaclear foam to fit
Ohh, I also use this foam to baffle filters. Stick it where the water flows out of the filter