Hey Ted,
If your pond water's turbidity is indeed caused by clay, then the gypsum in sheetrock will clear it up. Some ponds require a lot of gypsum to clear them up, others take a lot less. If your 4.5a pond needs more than a minimal amount per acre, you had better have a LOT of sheetrock scraps!
The smaller you can break up the sheetrock, the quicker it will dissolve and start to clear the water. Soaking and peeling the paper off should also speed up the process.
You may want to try about 1/2 tsp of sheetrock in a 5 gallon bucket of pond water before you do a lot of work. It should clear it up over night.
Good luck, and please keep us posted!
