I am very curious to know haha. The amount of questions I ask on here, you would think I don't know anything about fish Thanks!
its the place that gets the most oxygen and flow of constant water...and the filter media is very easy to attach to so its where the main bacteria builds its colony..at least thats what i was told over many years ago lol
Bacteria will colonize on just any surface it has available, and the more porous, the better, since that means more surface area at the microscopic level. Filter media is intentionally designed to maximize surface area, and is placed in an area rich in oxygen, which makes it an ideal spot for colonies to grow.