I've got 2 Eheim filters on my tank.
Those "ceramic rings" are possibly Ehfimec. That's your mechanical filtration.
Just use those and Ehfi Substrat Pro for biological filtration, no carbon. You could also use a filter pad with it.
Cabron is useless as hell, and even the story about carbon causing HITH is true, since I've experienced it myself. Carbon in the tank, Jack Dempsey got HITH, removed carbon, HITH gone.