Aquatic Control in Seymour, Indiana, 1-800-753-LAKE, URL
www.aquaticcontrol.com, sells a product called "Lake Kleerant" which is aluminum sulfate. It includes baking soda for addition as a "part B" to keep the pond from becoming too acidic. You dissolve it in water and broadcast it over the surface of the pond. I had a clay pond with essentially zero visibility due to ionically suspended clay. I applied the aluminum sulfate, and within a day or two had several feet of visibility. It has since stabilized at about 3', which I consider plenty.
