Kent Marine Nitrogen SpongeAmmonia & Nitrate Adsorber KENT MARINE NITROGEN SPONGE is a granular zeolitic medium that directly adsorbs ammonia in freshwater and fosters anaerobic bacteria growth to reduce nitrate levels in both marine and freshwater aquariums. Directions Use 1 cup for each 20 gallons of aquarium water. More can be used for greater effectiveness. Rinse with fresh water before use (preferably reverse osmosis or de ionized water). Place in a large mesh bag (800