That's a great setup!
I googled salt bath melt temperature and figured that potassium nitrate was what you were using. Table salt melts at about 800°C so would be way too high for this.
You may be able to get potassium nitrate from a butcher supply store as it is used to preserve meat (corned beef, for example). That's where I got some when I was a kid to make black powder! :grin: