Salty's,
Be careful,
hyposalinity (the salinity is lowered to 1.009 of gravity) is a very effective treatment for parasitic conditions such as Marine "Ich" but invertebrates cannot tolerate low salinity and should be removed from the tank. Or fish to another tank...
Another treatment option: freshwater dips - are a highly effective form of treatment against ich.
For some reason, many of us are nervous about freshwater dipping their fish; yet do not have any problem about using chemicals or toxins for treatment. Yes, I was one of them ready to use some staff from KENT and I’ve killed my wet/dry filter for weeks.
If a fish dies a day or two later, it is more likely that the fish too damaged to survive.
Take RO or DI water, aerate for an hour to maximize dissolved oxygen, heat to match the temperature of the dip water to that of the tank water, and then add buffering compounds to match the freshwater pH to your saltwater pH.
The aeration should continue throughout the dip. It is crucial to match temperature and pH and to maximize dissolved oxygen.
I used 10 gal glass aquarium so you can watch the fish - any dip less than two minutes is useless. Many fish will easily tolerate five, ten, even fifteen minutes or more. The least tolerant fish are wrasses, lionfish, pufferfish.
:happyfish