biOrb Ceramic Media is the biological part of the filtration process,as the aquarium cycles, the media slowly gets populated with beneficial bacteria, which makes your aquarium easier to care for Weight 450 Grams. Bought to use for Grandsons Goldfish Pete but we found him a New home. Never used. We used Glass Stones. Note - Took Media bag out for pictures only. (tore tab on box a little) See Back of box pic! NEW in Box!