Nice FRT, aquarium salt is fine but i wouldn't convert to brackish. They likely can tolerate mild brackish conditions but ideal would be hard fresh water. Sounds like what's comming out of your tap is at a good level so I wouldn't mess around with it!
There's no such thing as 'captive-bred' FRTs. The US has banned importation of FRTs since their exportation point would have to have illegally exported (aka: smuggled) the species in the 1st place.