This composite sediment cartridge is the pre-filter for model FM-2 CTO. It is designed to trap dirt rust and sediment. The SQC(sanitary quick change) design allows for quick and easy cartridge change. The Water Factory 47-55712G2 cartridge is made from FDA (CFR 21) compliant materials. Click here for information about the carbon block post filter 47-55708G2. Click here to purchase the FM-2 CTO cartridge replacement set.