Melasti is a purification ritual that takes place every year, usually in March or early April, precisely two or three days before the Bali-Hindu New Year day of Nyepi (the Day of silence). In 2012 it Melasti will take place on March 20. But there are some areas in Bali that establishes Melasti on March 19 night.
The bottom line is Melasti ceremony to purify ourselves, including a ceremony to purify the tools or sacred symbols.
See also Nyepi.