AquaCity&Atilde;&cent;&Acirc;&bdquo;&Acirc;&cent; 250SB Bio Balls Filter Media for Aquarium Fish Tank Pond Filtration by Aquacity 1" Ball in diameter; approx. 250 balls in 5 mesh bags; Good to use in both fresh & saltwater tank; offers mechanical and biological filtration with inside sponge. These bio balls are lightweight and typically float. They float so that the surface area can be close the air so that the bacteria get oxygen to thrive. Bag size: 8" x 5.5"