Weird white spots on concrete around pool

Got a mysterious problem with concrete staining. Hundreds of small white spots all over concrete- popped up one day. Tried power washing it but did not resolve. Doesn’t look like typical bird poop but that’s my best guess. But hundreds of small spots. Almost looks like white paint and only on certain spots on concrete and not grass, etc. see photos. Any thoughts on what they are and how to clean up?