Angel did most of our research and found they are more native to inland fresh waters, but can live in SW just as well (provided the leaves are rinsed of salt creep regularly).

I'd say put the brackish tank up and try it... what's the worst thing that could happen? You get tired of it and salt it up more and turn it into a reef with Mangroves? LOL

Eventually the goal is to grow these guys up tall enough to decorate around the spa, wether that will actually happen remains to be seen, but in the mean time they are just doing their thing.