(6 Pack) Aqua Clear Activated Carbon Filter Insert for 20-Gallon Aquariums (3 Filter Inserts Per Pack / 18 Total Inserts) Convenient 18 pack. (6) 3pks Adsorbs odors, discoloration and impurities Designed to fit the AquaClear 20 filter Suitable for aquariums between 5 to 20 gallons 3-pack; Economical way to purchase inserts