update: I added 2 tablespoons of gypsum to a 1 gallon jug of clear water, I then added about 12oz. of the slurry to a 1 gallon jug of pond water. 12 hrs. later the pond water was crystal clear \:D ! So, now i need to know how much gypsum to add to my pond? Its about .25 acres and 4-5 avg depth.