Summit's Calcium Montmorillonite Pond Clay 1 lb bag naturally clears koi ponds of organic waste particles that can cloud the water. When applied the pond clay binds to harmful impurities that can then be removed through the pond's filtration system, making the water crystal clear. The minerals and elements in these clays, when ingested, help the digestive system of your fish and naturally improve the colors and skin quality of your koi and other fish.