Zanyzap's Nitrite Remover Pads for Rena Filstar xP aquarium filters provide effective chemical filtration for freshwater and saltwater environments. The nitrite resin infused pads are designed to trap floating particles such as debris, waste and food, as well as reducing the amount of nitrites found in your water. These nitrate remover pads are great to use for preventing fish loss, outbreaks or chemical spikes. Replace with each water change, monthly, or as required after water testing.