I think some of the answers may be in this thread (see link below) if you start reading from the beginning. I'm impressed at several threads that document how well the right amount of Alum plus the pH buffering affect of calcium can clear a pond and keep it clear.
The exact answer for your situation can come from Rainman if you give him an idea of how big your pond is, average depth, how much water and then what your chemistry is in the pond.
Give some thought also to what is stirring up the clay and keeping it suspended in the water (water flow, rain run off, catfish, crayfish, or just who knows why?)
Alum vs CLAY!!
