Bill if you have a natural or fertilizer induced plankton bloom then trying to clear the water of plankton with alum or gyp. for esthetics is at cross purposes (clear water vs. fertile productive water) and may not work as per the above link. Cooler water temps will usually reduce the plankton bloom's density and the water will clear. Water quality is very important to all pond goals whether you want green water with lots of fish growth or gin clear water for swimming. There is info here on the subject and a series of PB mag articles in progress on the subject. Learning about how your pond water works is an interesting journey and is unique to your pond. It takes time and knowledge to understand how it works and responds to what you do. Good luck and post what you see and do and how it works. After about five years I began to have a good feel for our ponds and how they work and react.