| The Rena Filstar XP Phos-Zorb pouch contains a special filtration material that selectively removes phosphate and silicate, common nutrients found in fresh and saltwater aquariums. In saltwater aquariums, excess phosphate lowers the available calcium and magnesium necessary for the growth of hard corals and other invertebrates. In freshwater aquariums excess phosphate provides nutrients for the growth of unsightly algae. Keeping the phosphate levels low will reduce your maintenance time help maintain crystal clear water. |