TKD, I assume you are trying to clear a muddy pond...? Have you looked for, or know the souce of the muddy water?
Gypsum only works about 40-50% of the time to clear a pond. The usual way to spread it (or ag lime) is a floating dock or platform, pile on as much gypsum and use a trash pump to blast the gypsum off into the water as you troll around the pond. Alum is 100% effective and usually less costly.
