Rinse pouch under tap water. Place pouch in path of water flow in the aquarium filter. Activity of the pillow lasts 48 hours. After 48 hours, recharging is necessary. To recharge: dissolve 3 tbsp. of API AQUARIUM SALT in 7 oz. of tap water. Rinse pouch in tap water, then soak in salt solution for 2 hours. Place back in filter. When not in use, store pouch in recharging solution; do not let pillow dry out. Replace when pillow ceases to function properly after recharging.