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