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