Specifially desgined for Fluval 306/307 & 406/407 filtersEffective at removing and reducing nitrite Effectively traps floating particles for clear water (debris, excess food, and waste) Supports beneficial bacteria for a healthier aquatic environment Custom fit to increase filtration efficiency For best results, replace monthly or as required after testing water with your Fluval test kit Convenient 6-pack format For use in freshwater and saltwater aquariums