Welcome , Jeff to the PB forum. Here is some info on water ph and fish from SRAC.

The recommended
pH range for aquaculture
is 6.5 to 9.0 .
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 ( high alkalinity).
Pond pH varies throughout the
day due to respiration and photosynthesis.

Also most FH die after a full year's spawn ( avg. life span 15-18 mths).