1 grain/gal = 17.1 ppm
What she is quoting is the GH .... for fish & pH stability, what you want to know is the KH, although GH & KH usually goes together, it is not always the case.
What is happening with the pH swing is from spring runoff. Denver's water would be naturally hard (being in the mountains), but snow (& rain) is almost pure water, so adding a lot of that to the water will dilute out the KH & GH. We get the spring runoff effect here as well, but not quite so extreme as we are a hundred miles out of the mountains.
Generally, water with pH of 8 should be well buffered & fine for your fish. However, should you find major swing during spring (say pH down to 7 & KH of nothing), you might consider buffering the water with some crushed coral in the tank. CaCO3 (ie cc) naturally drives the pH towards 7.8. It won't do anything to the water in winter with a pH of 8. But when you add pure water during spring, it will dissolve in & keep your pH constant.
The only way to tell if this is needed is to wait till you've moved & see how much of a swing there is during spring (or talk to some aquartist in Denver.) I don't know about the other fish, but for Goldies, a pH drop during spring runoff/rain is part of the natural life experience and is a signal to the fish to spawn. They can tolerate a 0.2 pH shift daily, so as long as you keep your water changes small & frequent, you should be fine with what we know of the local water. <OTOH, cc is a good insurance, and if you keep the temp & pH constant, you won't have to deal with spawning goldfish.>
