In a pond with less than 200 ppm alkalinity I have never heard of a negative consequence to adding ag lime. The higher the alkalinity up to and above 200 ppm the less daily ph fluctuation and the less stress on fish.

Fish and other vertebrates have an
average blood pH of 7.4. Fish blood comes into close contact
with water (1- or 2-cell separation)
as it passes through the blood vessels
of the gills and skin. A desirable
range for pond water pH
would be close to that of fish
blood (i.e., 7.0 to 8.0). Fish may become
stressed and die if the pH
drops below 5 (e.g., acidic runoff)
or rises above 10 (e.g., low alkalinity
combined with intense photosynthesis
by dense algal blooms –
phytoplankton or filamentous

A desirable range of
total alkalinity for fish culture is
between 75 and 200 mg/L CaCO3

Last edited by ewest; 05/17/11 09:17 AM.