Some additional information on pond liming.
Liming ponds Quote from the above article:
"It is difficult to add too much agricultural limestone to a pond. At a pH of 8.3 or greater, calcium combines with carbonate to form limestone and drops out of solution. Limestone does not dissolve well in ponds where soil acidity has been neutralized and water pH has stabilized at or above 8.3"
"If high volumes of water regularly flush through a pond, the agricultural limestone, agricultural gypsum or calcium chloride that have been added can be washed out. Often more than the recommended amount of limestone or gypsum is added so the materials will not have to be applied as often. These chemicals will not cause problems in a pond if added at two or three times the calculated amount."
