CNZ&reg; 50pcs Black Aquarium Fish Tank Filter Bio-Balls Filtration Media, 1-inch Free media bag for easy handling BIO-Balls do not require replacement unless damaged or destroyed bio-sponge inside provide more surface area for growth of beneficial Bio-Spira bacteria In the event of excessive buildup, you may gently rinse with water from an established aquarium, if desired Diameter of bio ball: 26mm (1inch)