instead of sacrificing anything. And since theres nothing in there other then fish. Try Hypo treatment. This is the best recommended treatment to all fish IMO, and obviously best for fish with no scales. Hypo is efficient, but does not always work. I however have had very good luck with it. All thats needed is to reduce the SG in your tank, slowly to avoid shock, until your at that magic number. For all of my treatments i use an SG of 1.009 This does not hurt fish as its less work for them to export nutrients from the water, etc.... This will also kill of external parasites.
if your having something more serious, along the lines of an internal issue then meds will be needed.
good luck, and google Hyposalinity treatment for more information