Acidic coffee due to water hardness?

Hello to all of you,

I just bought a used Jura D4 coffee machine, in perfect condition. It would have been used only a few times before.
Before taking it home, I made a coffee at the buyer's place, with beans brought by myself. Without even making any adjustments, the coffee was simply perfect.
When I arrived at home, I quickly made an espresso for myself and my wife, with the same beans, and there, it's the drama: the coffee is suddenly acid, so much so that at the end, it leaves an impression of... lemon juice.
The only element that has changed is obviously the water. At home, the hardness test shows 2 colored squares out of the 5 possible. I deduce that my water is not very hard, therefore not very calcareous, therefore more alkaline than acid. So I bought bottled water with a high ph, but nothing helped. I also played with the grind, bought a softer and rounder coffee, roasted in the morning...Still the same.
I know, for having lived there, that the water of the city where I bought my machine is very calcareous (presence of tart in the kettle, the water heater...)
My research on the Web does not bring me more tracks of research
.
And I'm a bit... disgusted (literally) by my coffee.
Any help, any advice from your enlightened taste buds are welcome.

See you soon,

Michaël

There were other beans in the grinder when I tested it, the ones I brought myself only come through in the second coffee. Set the brewing temperature down, if possible.

If you mention "taste like lemon juice" then I would guess that the previous owner decalcified the machine with citric acid and that this may have only become noticeable at your home. You could try a few passes of amidosulfonic acid descaler (e.g. ceragol Premium Descaler) to get rid of the taste.