According to my water department, my water profile is as follows:
Calcium: 3 mg/l
Magnesium: 0.6 mg/l
Sodium: 4 mg/l
Chloride: 5 mg/l
Sulfate: 9 mg/l
Alkalinity (as bicarbonate): 3 mg/l
These numbers have predicted my mash pH pretty well with Kai's water calculator. However, I just tested my water with an aquarium GH/KH test kit, and got 89.5ppm GH and 71.6 KH. What's going on?