JUWEL Nitrax is a biological filter medium to break nitrates down in your aquarium. It reduces the growth of algae and promotes the vitality of your plants and fish. JUWEL Nitrax reduces nitrate levels in your aquarium, leading to a considerable reduction in algae growth. Nitrax is a biological filter on the containing specialist microorganisms to break down poisonous metabolites (ammonium/nitrite) in your aquarium, thus reducing the danger of fish mortality. Nitrax also reduces algae growth by anaerobically breaking down nitrate, thus supporting the vitality of your fish.