Just found this on Aquaria Central:
"The young fishes are adaptable to freshwater, but with age they need to be kept in more and more salty water to do well. Eventually adults (over 10 cms in length) need water of salinity close to seawater (specific density 1.010 upwards). Adults are much more shoaling fishes, and restlessly swim up and down the tank. This can be disconcerting to some, more placid, fishes. Both species benefit from hard, well buffered water and the use of a protein skimmer and UV sterilisation helps to keep the adults healthy. Fluctuations in salinity are also useful, but care should be taken during water changes not to stress the fish."