Juwel Nitrax M Compact Nitrate Sponge for Bioflow M (3.0). The sponge is designed to reduce nitrate levels in the aquarium. This in turn helps reduce the amount of algae and helps provide a more healthy aquarium for your fish and plants. Nitrax is also a biological filter containing specialist microorganisms to break down poisonous metabolites in the aquarium. It’s recommended to change the Nitrax sponge every 2 months for optimum performance. Suitable for JUWEL Rio 125, Rio 180, Rio 240, Vision 180, Trigon 190, Lido 120 & 200.