The hardness, both GH and KH, could be higher than 180 ppm each as that's as high as the tester goes.
JLawson lives quite near me and with the same water supplier, and I have soft water. Unfortunately, in the last couple of weeks this water company had changed it's website and no longer gives hardness. (There is a box which looks like it should be a link but nothing happens when I click on it)
I would be inclined to take a sample of tap water to an LFS and ask them to test GH and KH. If they use a liquid tester, that will measure higher than the strips and probably be more accurate.
But I do need to check - is there anything in the tank that could be raising GH and KH? Something like coral, limestone etc?