Hyposalinity treatment should be used for fish only, as it would be extremely stressful on corals. There are a few instances where people use a fresh water dip for corals, but only when finding parasites. Depending on the type of corals you are acquiring, I would thoroughly inspect them before going into QT, and watch them closely while in QT. As an example, on zoanthids, you want to look for things like small white spiral egg cases, sundial snails, and zoanthid eating nudibranchs. For acroporas, you want to look for things like red bugs and acro eating flatworms. For montiporas you want to look for monti eating nudibranchs. There are non specific things to look for, as well, such as Convolutriloba retrogemma flatworms (sometimes referred to as red planaria flatworms).