Well riccia can survive at low light so thats not a problem, its really a question of how well it would do in a brackish tank, riccia usually does best with added co2 and to make it pearl would require a lot of light, it might do best for you if you let it float for a while to grow nearest the light (piece of airline hosing made into a loop can keep it together and stop it floating all over the surface) and then you could tie it down to slate or whatever and submerge it when it has grown out a bit which doesnt take long with riccia, but IMO it will survive ok unless the light is very low.
