JesmondJester - Still doing exactly that. I’m not that precise on numbers though… If it ends up being 120mg or 90mg per litre I don’t really worry too much.
I’ve been using potassium bicarbonate for the past year. I can’t tell the difference, but I might as well use it up since I got some.
For what’s worth, my tap water TDS is approx. 200ppm. I’ve been using the same filter since May 2023, and, last week, the TDS meter registered 1ppm on my “pure” water. The instructions say to change when the TDS meter reads 6ppm.