Specifially desgined for Fluval 306/307 & 406/407 filtersEffective at reducing and controlling toxic ammonia spikes Effectively traps floating particles for clear water (debris, excess food and waste) Ideal for new and heavily stocked aquariums Use after medicating fish Custom fit for 07 and 06 series filter to increase filtration efficiency For best results, replace monthly or as required after testing water Convenient 6-pack format For use in freshwater and saltwater aquariums