Dr. Don, one of the great things about calcium carbonate ag lime (dolomitic) is that it's impossible to overdose a pond with it. The highest the ph can go is the ph of the lime, usually 7.8 to 8.4, which is a safe range even at the high end. Since it is not very water soluable, there is no danger of a rapid ph change like you will get from slaked (hydrated) lime which is extremely water soluable. Too many variables come in to play to say how long a lime treatment will last but generally it will last 3 to 10 years.
