Howard it depends on what the alkalinity scale is. I have never seen one go to 720. If it is in ppm (parts per million) or mg/L (milligrams per liter) then 170 is great and you don't need lime. 500 ppm is very high (soda water)
Ideally, an aquaculture pond
should have a pH between 6.5 and
9 as well as moderate to high total
alkalinity (75 to 200, but not less
than 20 mg/L) and a calcium hardness
of 100 to 250 mg/L CaCO3.
Here is a good fact sheet.
http://srac.tamu.edu/tmppdfs/173593-471f...bd31dc4777c3918
.gif)
