I had a similar size pond dug here in Michigan 4 years ago, it too was clay. My pond took about 2 years to clear up. I tried the gypsum thing and watched water in a jar, but the only thing that helped was time and getting the shoreline seeded to hold back sediment when it rains. Since I have had decent grass and clover growing around the pond washing in clay during rain storms is no longer a problem. I know it's hard, but be patient, it will clear-up with time. Note: my pond is not crystal clear, but clarity to a depth of about 2 feet is very good.
