White stains on tile

[newbie2017]

Does anyone know what these white stains on the tile are? I noticed these a couple of days back.

Thanks.

 

[mknauss]

Efflorescence through the grout lines. Moisture comes through the earth/concrete behind the tile and exits bringing minerals with it. The moisture evaporates leaving the minerals.

Typically a dilute muriatic acid solution applied to it will remove it.

 

[newbie2017]

Thank you.