Re: Efflorescence, Latex Leaching, or what?
I agree, it looks like efflorescence, but given where it's at this should NOT be the case. Efflorescence comes from moisture wicking through cement, bringing with it the minerals trapped within. This is most commonly seen in basements with earth contact on the outside and high water tables. You should not have this problem on a bathroom wall, especially if over drywall.
It is possible that high humidity could be pulling the salts through the grout, but even that seems very unlikely.
I suffer from CDO ... Its like OCD, but in alphabetical order, LIKE IT SHOULD BE!!!