Hydor Bio-Rings for freshwater and saltwater aquariums are created through the high-temperature sintering of inert quartz. Thanks to the macroporous structure, Hydor Bio-Rings is the perfect media for biological filters where the main goal of the hobbyist is the development and growth of beneficial bacterial colonies. (aerobic and anaerobic) on the large surface area available(8.25 meters squared per liter) Bio-Rings does not release phospates, heavy metals and does not affect the pH of the aquarium.