Product FeaturesGACGranular activated carbon for removal of chloramines, tastes, odors, and chemicalsKDF 55KDF 55 media removes numerous heavy metals, including lead, mercury and iron and aids in the removal of other contaminants.5 pounds KDF55Higher KDF amount for tougher problemsBig Blue 20"Filter measures 20-inch long and 4.5-inch in diameter.Standard Big Blue SizeFits in all standard 20" Big Blue filter housings.Product DescriptionReplacement GAC/KDF 55 filter fits standard 20" Big Blue filter housings. The is a great upgrade to standard GAC filters or carbon block filters. Used in conjunction with a sediment filter and/or carbon block filter, the system will provide a wide range of treatment. Typical life expectancy varies greatly depending on water parameters and usage. Recommended replacement is at leastonce a year, with every six months typical.