my tank is very soft (based on city water info), and alkaline (pH~8
according to my LFS.

That's odd. Soft water is usually acid, hard water is usually alkaline.

Our local water supply has the following numbers from the city's webpage):

gH = 82ppm = 4.6 degrees
kH = 52ppm = 2.9 degrees
pH = 9.7


--
Victor M. Martinez

http://www.che.utexas.edu/~martiv