Aquarium Ion Exchange Water Softener for Hard Water Fish Planted Tank (300g) removes calcium and magnesium cations / stable pH level Exchanges cations with resin. It effectively removes calcium and magnesium cations. Softens water and maintains a stable pH level. Best water treatment for soft water fish like Discus, Neon, Dwarf cichlid, Betta... etc. Provides the ideal environment for plant ecology. The media is packaged in a net bag (as seen in the photograph).