This is from a different forum, but is what I was told when I looked onto our water (I'm in Clawson, by the way

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A GH (Total Hardness) of 104ppm (= mg/l) would be 5.8 or say 6 dGH. The Alkalinity or bicarbonate hardness (KH) of 76ppm would be 4.2, say 4 dKH.
This is ideal water for most soft water fish. The pH should naturally lower as the aquarium's biology becomes established.
So, what I learned is that when discussing the GH mgl/L is equal to ppm, and that number is then divided by 17.9 to get the dGH.
The good news is that a very large area around us gets it's water from Detroit, so any local fish should be used to it.