This one filter bag of ceramic rings, provides a higher cumulative pore volume per liter than standard biological media. They are highly porous, with hollow design, effectively distributing water flow and allowing massive colonies of "biological filter" bacteria to grow on and inside each ring. They are an ideal substrate for growth of nitrifying bacteria that removes toxic ammonia and nitrites. They will not allow break down, or alter pH or water hardness. Rings will become colonized within several weeks. One liter treats 75 gallons.