The చంద్ర vrat is kept on సోమవార — traditionally one meal after sunset, without salt. It is the household remedy for a weak చంద్ర, and unlike a gemstone it cannot be kept against your chart.
The weekday fast is the household remedy — kept on the graha’s own day, usually one meal after sunset and no salt. It is as much a discipline as a ritual: the point is the weekly act of restraint, held long enough to mean something.
The Monday fast — one meal after sunset, no salt — is the classical Moon fast, and Purnima and Pradosha fasts strengthen the Moon too.
An afflicted Moon reads as overreaction, low mood, thin sleep and a general sense of being unsettled. Monday observance, Shiva worship and time near still water are the standard responses.
సోమవార. Fasting, charity and mantra japa for చంద్ర all belong to that day.
The mantra, the weekday fast and the charity are safe for anyone — they address చంద్ర without amplifying it. మోతీ is not: a planetary gem strengthens whatever the graha is already doing, so it needs a chart reading first.