I wasn't trying to down play you experiences or research, WYite, or your treatment suggestion. Most of my loach etc. females-always-gravid experiences has been in pretty low TDS but at different pHs, neither very high, say 7 to 7.6-ish Since most loaches are still wild caught...well, do we act like...what, they can't adapt to other parameters? I truly don't know. I do know a Brit with pretty hard water has bred many, many loaches...in much harder water than I've ever had or are "native" to them...so maybe it's something else...No ready & willing male comes to mind, maybe males need LOTS of time to mature?
But a lone female without a male...I've had rams & angels & some other fish lay eggs, diliberately, not just expelling them, but that sometimes seems like a last ditch effort before they soon die (sniff)...I dunno...