pH again
I do have a problem with this whole thing, I've said it before and I'll say it again here. The quantity of vinegar which will convert your pH 6.8 well water to a moderately acidic pH 5.5 or so (1 tablespoon to 5 gallons) will have almost no effect on really hard water. The sums don't add up. Whatever Elton is doing or seeing, it isn't because he is converting hard water into acidic water, he just isn't using enough vinegar.
--ian