Bulk Reef Supply 7 Stage Reverse Osmosis Dionization Filter kits include everything you need to get your 7 Stage RO/DI System running like it is brand new again. We have options that pair our PRO Series Deionization Resin with either our BRS Universal Cabon Blocks, or Matrikx CTO and CTO+ Carbon Blocks. The PRO Series Deionization resin allows you to change only the resin that is used by your water, saving a lot of money in the long run. Each filter kit includes a sediment filter, two carbon blocks, and PRO series resin. Both the sediment filters and carbon blocks replace the old filter, where the resin actually needs to be repacked into the original resin cartridge that was included with your BRS RO/DI System. We suggest packing DI resin as tightly as possible into the refillable cartridge to help prevent channeling that can allow the water to essentially bypass the resin.