I fill all my systems with Evian, after millions of years of filtration through volcanic regions it's good enough to drink and no inhibitors needed.
It also meets your own requirement that it does contain some pH.
Two bottles of Buckfast is generally all that's required in the average system, it's the correct chemical formula & on a par with most inhibitors on the market.
Of course I can't advocate taking so much sugar in ones Tea, on medical grounds.
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