As long as the tank is strictly FO, with no inverts, crabs, snails, LR, LS, yes you can perform hyposalinity safely.
However, in that size tank, you will be doing MAJOR water change out to get the salinity down to the theraputic level for hypo, and then, 3 wks later, another major water change to return the salinity to within normal range. The process of dilution and reinstatement of salinity is not as easy as you might think, particularly in that size tank.