LiquaGen - Replacement Aquarium Reef Mixed Bed Color Changing Deionization Resin (RO/DI) for 0 TDS/PPM Water - MBD - 30 This product is a great replacement part for aquarium systems, laboratory testing, and other applications where ultra-pure water is necessary. The supreme anion resin is a Type I strongly basic gel resin with an indicator dye that changes from green to light brown as the resin exhausts. This makes it easier to know when to replace the DI. Comes in air-sealed multi layered packaging to ensure a shelf life of 1 year Super easy & convenient installation