Yeah, hard water shouldn't be that big of a deal unless they're attempting to breed soft water fish or anything. Here in central Ohio, the tap water most places is basically liquified limestone, but I've kept tetras, angels, and blue rams in it. I just stick to breeding fish like Rift Lake and CA cichlids that come from this type of water. If they really want a good, long-term solution, they should try using R/O water. If it's just one or two small tanks, they could buy the water to mix with their tap water, or if it's a big tank or several tanks, it would probably be worth while to invest in an actual R/O unit to filter the water themselves