JUWEL Nitrax reduces nitrate levels in your aquarium, leading to a considerable reduction in algae growth. Nitrax is a biological filter containing specialist microorganisms to break down poisonous metabolites (ammonium/nitrite) in your aquarium, thus reducing the danger of fish mortality. The Juwel Nitrate Removal Sponge contains bacteria, which will after a while reduce the nitrate level in the aquarium significantly. Having removed the nitrates, which is the nutrient for the algae, they will starve or not even start to develop of this in turn will enhance the vitality of fish and plants. Using the Juwel Nitrate Removal Sponge can mean that the partial exchange of the aquarium water can be extended to 4 weekly intervals. In order to allow a proper level of micro-organisms in the filtration system it is recommended to exchange the sponge every 6 weeks.