As many readers have already told you, the bacteria in the tank won't be of much help if you switch to freshwater, BUT, if you rinse it well, the sand should be fine to use in an African Cichlid tank. Lots of cichlid keepers used to use fine crushed coral in their tanks as a buffer, pumping up the pH and carbonate hardness for their little beauties...
Definitely check into that further, as the practice MAY have gone by the wayside along with undergravel filters...
Cichlid-Forum ::