Regenerative, alkaline anion exchanger with high nitrate selectivity. Binds residual nitrates in the permeate (pure water in the reverse osmosis system). Removes nitrate directly in fresh water aquaria. 1,000 ml bind up to 60,000 mg of nitrate. Duresin N can be placed directly downstream of a reverse osmosis plant in a separate filter casing (e.g. filter casing FG 500). In the aquarium, Duresin N has the best effect if it is used in a net bag in the filter system.