IceCap's Bio-Sphere Pellet is made up of small ceramic spheres in a compact three-quarter-inch pellet, providing up to 5 gallons of efficient biological filtration for both freshwater and marine aquariums and ponds. This media offers an ultra-high surface area, ideal for the colonization of beneficial bacteria, and can be used in various filters or directly in the aquarium. Each 1KG box contains 145 Bio-Sphere Pellets measuring at 3/5in x 3/5in.