If you can remove the fish to a QT tank, say a 15gal tank, here's what you do:
Fill with tank water. Over the next several hours, lower the salinity of the tank to a 1.008 sp. gravity. Be absolutelysure you have a properly calibrated measuring instrument. A plastic swing arm I can guarantee you will be so far off that you will kill the fish. You need to calibrate against a known solution. See here for how
to make one:
http/www.reefkeeping.com/issues/2004-06/rhf/index.php
You need to keep the fish in this QT for 30 days with no spots. If on day 15 you see spots, you start the clock over.
NO rock in the QT. Put a large piece of pvc or something like that for the fish to hide in. No lighting needed either.
You must test the water daily. Any evaporation will raise the salinity. Topoff is essential to keep the level and thus salinity stable at 1.008. If it goes over, the ick will attack the fish again.
30 days.
Feed a mix of M.Y.S.I.S. (company initials are P E I forget their name.) Into this, add the following according to their instructions: Seachem Focus and Seachem Metronidazole, and saturate with one of the garlic additives -- may as well use Seachem's. Kent's is good too. Best is to melt the fozen food in a bit of water, enough to soften it, add the meds, and re-freeze. I would add also spirulina flake, or Formula Two flake, before re-freezing. Feedt his and only this the entire time.
By the time the fish is 30days spot free, the display ought to be ready to add him back.
Unless you have fish in there still. In which case, ich will be there too. But the tang should get stronger and maybe it'll fend off upon reintroduction.
Oh, after 30 days you have to raise salinity by one point per day until it matches the display. When it matches, reintroduce the fish. No acclimation necessary as you will use tank water to adjust the QT.
If spots reappear during this, back to the regimen.
If you wish not to use tank water you can raise with fresh but then you may have more stress to the fish on reintroduction.