if they are T. microlepis then it is ok to keep them in freshwater but it needs to be hard water not soft.
the way to tell is the dorsal marking. In t. jaculatrix and t. chatareus, the dorsal strip will continue from the body up onto the dorsal fin and be connected. on T. microlepis the strip is broken into two, one portion on the body, and then a break on the body-fin interface, then the marking appears again on the fin.
It is subtle but accurate.