The Rena Water Softener Pillow Removes hard water minerals and toxic heavy metals from aquarium water. Provides continuous removal of minerals and heavy metals. Recreates the soft water found in tropical areas where many aquarium fish come from. Label Instructions: Flatten the pillow to evenly distribute the resins within. Place the pillow directly in the filtration basket. Activity of pillow lasts 48 hours before recharging is necessary. Ingredients: Special ion-exchange resin. Sodium ions are exchanged for heavy metals calcium and magnesium. Does not add salt to aquarium only harmless sodium ions. Chemical filtration device. Use one 400 gram bag for every 20 u.s. gallons (75 Litres).