Boyu CR-500 Bio Ceramic System Rings provide ideal surface area for beneficial bacteria colonization. Highly porous and hollow to effectively distribute oxygenated water. Colonies of nitrifying bacteria grow on the outside of these rings, removing toxic ammonia and nitrites. Suitable for freshwater, saltwater fish tank. High permeability, which can be aerobic nitrification and anaerobic denitrification, to make the water more stable, is the best biological filter material. Boyu's CR-1000 biochemical ceramic rings with phytocide abilities protect your aquarium life through aerobic nitrification and anaerobic denitrification function, providing a habitat for large colonies of beneficial bacteria to thrive on a surface similar to the natural environment of micro-organisms.