Aquapapa SB4000 1" Bulk Biochemical Bio Balls with Inside Sponge Design Filter Media for Aquarium Fish Pond Fountain Waterfall Filtration, 4000 Count Ball size: 1" in diameter These 1" polypropylene Bio-balls are great for your canister filter or fish pond filtration. With inside Bio sponge design, they provide large amount of surface area in a small space where lots of beneficial bacteria can form on the surface. Nitrifying bacteria help remove and convert toxic waste like ammonia and nitrites from tank water. Our Bio balls are lightweight and typically float so that the surface area can be close the air so that the bacteria get oxygen to thrive. Approx. 4000 pcs in the package.