Biological filtration is accomplished by promoting the growth of beneficial nitrifying bacteria within the aquarium filter or refugium. The beneficial bacteria convert toxic ammonia and waste proteins into nitrates that are more easily removed from the aquatic ecosystem typically through filtration. Although compact in size, Bio-Balls provide a large surface area for beneficial bacteria to grow due to the unique construction and geometric design of the one inch round balls. Typically used in sump filtration systems, Bio-Balls are a good choice for adding biological filtration to your aquatic system.