PhosGuard removes phosphate and silicate from marine and freshwater aquaria. Great for use in many applications, including power filters, canister filters, and wet/dry filters & sumps. It is not recommended for phosphate buffered freshwater. This product is highly porous for high absorption capacity and bead shaped for optimum water flow. It outperforms all competing products. PhosGuard is not an exchange resin, it does not release anything into the water.