Is this efflorescence?

[Fluorescent_Frogs]

Only shows up in the middle of the tiles. Seems to disappear when wet, but as the tiles dry out it comes back. It’s a hard chalky white substance, doesn’t brush off. It’s only appeared in the last few months, as the weather gets colder.

Thank you!

 

[ajw22]

Waterline Scale Removal - Further Reading

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