The Bio-Filter balls provide a large, multi-faceted surface area for the growth of the beneficial ammonia-neutralizing bacteria responsible for biological filtration.??BIO-Balls are part of the C-Series Filter Replacement Media and Parts.??BIO-Balls do not require replacement unless damaged or destroyed. In the event of excessive buildup, you may gently rinse with water from an established aquarium, if desired. Do not clean with soaps or abrasives and never rinse with tap water.