In 'The New Marine Aquarium' by Michael Paletta it says, " As radical as it sounds the specific gravity of the quarantine tank may be lowered to the level of 1.010 to 1.012 and most fish will acclimate readily." This helps kill common parasitic diseases like marine ich and marine velvet and several types of problem worms, since these parasites have a much lower tolerance for decreased salinity levels than the fish do. However nonbony fishes like sharks and ray along with invertebrates will not tolerate these low salinity levels. Some experts simply keep their QT at this level as standard procedure.