Adding lime in an area of acidic dirt (watershed) is not a one-time event. I have never had anyone suggest discing it in. Using ag lime spread it as best you can over the pond bottom (perfect is not required). Once treated the lime will have a curve of effectiveness - it will take time several mths to get the water alkalinity up and will then stay that way for a while then start declining. Depending on location the application can last from 1 yr to 4 yrs. You are treating the water not the dirt. Lots of good threads on this. If this is a new pond /dry ground, then put twice as much as suggested. You will be saving some work by doing that.