The floor tile in the shower has a white spot

Hello

after one year, an anthracite floor tile has a white spot in the middle. As if it is "worn sore."

Is it normal for large floor tiles to have abrasion? It does not come off with common cleaning agents. It cannot be dirt.

A picture is worth more than a thousand words :)

I will deliver tonight to...

Maybe lime scale deposits because the shower head drips a little there? Have you ever tried Silit Bang or another strong descaler on it?

If [Kalkfleck] then [Klarspüler für die Geschirrspülmaschine] can also help.

Hello,

attached are the photos. It should not be lime scale.