Activated Carbon/Charcoal is a chemical filtration media that is mainly used to remove medicines (after treatment is over) from the water and remove tannins (brown tinged water from wood, etc). In planted tanks, it can remove some of the ferts we dose so that is another reason why people don't want to use it. It's just better to use it when it's needed, and you can fill the filter with some other type of media.
In place of the charcoal, you could add more mechanical media (sponges, polyfil, etc. - removes/catches physical debris particles from water) or biological media (Seachem Matrix, Ceramic BioRings, etc - houses beneficial bacteria to keep the water healthy by converting fish waste into safer forms).
Mechanical media can actually serve as biological media as well, but usually has less surface area, so it's less efficient (sponge filters are good).
The ceramic rings (assuming they are the porous rough faced ones, not the smooth faced plastic rings) are biological filtration media. They are decent, but Seachem Matrix has more surface area in comparison, so has more potential of housing more beneficial bacteria, in turn be able to support more fish. So I would get Matrix over ceramic biorings, but the biorings are still alright. Just thought I'd mention.