Sediment filters primarily remove dirt that clog your carbon blocks. Carbon blocks primarily remove chlorine that oxidizes and ruins your membrane. DI resin allows you to get ultrapure RODI water for your saltwater reef water changes. We recommend including at least one catalytic carbon stage if you are on well water OR if your city uses chloramines to treat your water. Text us @ 772-461-0256 with the name of who you pay your water bill to & we will look up your specific water quality report for you.