The PRO Series Purple Cation DI Resin is designed to be a highly efficient and reliable part of any reverse osmosis deionization (RODI) system, specifically as the first stage in removing cations from water. This resin changes color from purple to amber when it becomes exhausted, making it easy for reef aquarium enthusiasts to monitor its effectiveness without needing specialized test kits or equipment. It is perfect for those who want precise control over their water quality and are looking to achieve near-zero total dissolved solids (TDS) levels in their reef tanks, ensuring that harmful contaminants such as phosphate, silica, nitrate, sulfate, aluminum, iron, calcium, and others are removed before they can harm delicate coral life. The resin's sodium (+1), calcium (+2), and other ionic charge specifications make it uniquely suited to handle the wide range of potential impurities found in tap water after initial RO filtration.