Nitrax M Compact Sponge for Bioflow M Nitrate (3.0). The sponge is designed to reduce nitrate levels in the aquarium. This, in turn, helps to reduce the amount of algae and helps provide a healthier environment for your fish and plants. Nitrax is also a biological filter containing specialized microbes to break down toxic substances in the aquarium. It is recommended to change the Nitrax sponge every two months for optimal performance. Suitable for JUWEL Aquarium Rio 125, Rio 180, Rio 240, Vision 180, Trigon 190, Lido 120 & 200.