On 29/09/2019 17:11, Clive Arthur wrote:
We have a water softener, standard ion exchange type in which you put
salt blocks.

We still get some scale, though it's a much finer and harder scale which
is immune to normal descaling acids, so I'm guessing Sulfates.

A softener exchanges low-solubility metal ions such as calcium,
magnesium, iron etc for sodium ions, and *all* sodium salts are readily
soluble, including sodium sulphate.


Maybe you just need to turn up the setting on your softener (is it timed
or measured?).
It might be interesting to scrape off some of the scale, get it in a hot
flame, and see what colour you get - that might identfy the metal component.

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Reentrant