Eheim LAV Biological Filter Mediais a top of the line biological filter media created from natural volcanic rock, boasting an incredibly porous surface structure that encourages the growth and development of beneficial bacteria colonies. These bacteria will help to rid your aquarium water of dirt & debris as well as preventing the buildup of toxic compounds such as ammonia and nitrite. Well suited for both freshwater and saltwater ecosystems, LAV can be washed and reused as a way to extend the life of your filter media and your filter overall. As the media is natural, it comes in different granulate shapes and sizes.