Sometimes referred to as bio rings, Ceramic Rings are unglazed pieces of
fired ceramic. Most commonly, they resemble small white beads. However, they can
also be found in other colors like cream, gray or brown.
Ceramic rings are designed to have an outer part that has lots of small holes, or pores, and a central hole that goes through the entire thing. This way, water not only runs over the ceramic rings but through them as well.
Confusingly, the phrase ceramic rings is often used to describe any ceramic-based filter media, regardless of the shape – round, square, even those without holes!