On Fri, 29 Mar 2019 07:15:52 -0700 (PDT), condo owner
wrote:

Here are more photos:

https://st.hzcdn.com/simgs/c132db930...ome-design.jpg
https://st.hzcdn.com/simgs/459226720...ome-design.jpg
https://st.hzcdn.com/simgs/140228500...ome-design.jpg

I agree with Ed. Minerals. It could be leaching from the concrete or
from hard water.

See: Efflorescence https://en.wikipedia.org/wiki/Efflorescence

For grins & giggles, try soaking with some 6% White Cleaning Vinegar
and scrub with a good nylon or soft brass brush.

YMMV