@user2059078 Efflorescence can happen any time the cement gets wet, there's no way to tell if it's water from rain (normal) or from accumulated water due to inadequate drainage.

Eep! I found the code for single family units (I live in a townhouse) and hardwired smoke alarms are in that code, so they're probably in the multi-family home code as well (as soon as I find it). Thanks!

What was in the pilaf? That would help suggest the type of cleaner to use, though for a food stain I would probably start with an oxygen based cleaner.

Are there any "features" on that wall in the shower? That looks almost exactly like what happened to my shower because the waterproofing on the shower seat was installed incorrectly and allowed water behind the backerboards. When we dismantled the shower door (after 8 years of soaking), that whole strip of tile just fell off.