Very high water hardness
I just took a very crude hardness sample from our 10-stage water filter water, which corresponds roughly to that a professional lab gave a few years ago, when I wanted to know its capability for brewing water. Our water hardness is way too high for brewing purposes at 310-370+, as well as too alkaline, 320-326. (Note this is an average of city supply from 3 wells; weirdly, my hardness sampling just gave me 281 ppm, even though our rented unit is served with a (sodium) water softener. It didn't really matter as I know Na is very likely through the roof, in any event.
It was just terrible for brewing even dark ales. As a result I "built" acceptable water from DI and principally calcium and magnesium salts, or treatment with H2S04 and HCL (with acid use being more of a traditional British brewing thing, which was my practice - very traditional British brewing).
I know overly hard water can tighten up glutens (certainly haven't experienced this!) and depress fermentation rates. Thoughts? Leave it? Treat it? Start from DI and build by additions? Buy bottled water?