Did they tell you to treat the entire tank or just the fish. Formalin is a pretty nasty chemical and crosslinks proteins permanently (ie, kills the outer layer of tissue as far as it can penetrate). It is also extremely harsh on fish gills and that is likely why your fish are struggling. Granted only 2 drops per gallon isn't that much but most corals and anemones won't tolerate any chemicals at all.
A better recommendation would have been to remove the fish and treat in a separate tank.
Your scopas tang is probably ok but stressed, they often get a very dull washed out coloration after the lights are out (ie when they're "sleeping")and when they're stressed out.
What to do now? Run carbon (not sure if carbon gets out formalin but it will help clear the water). See how things go and possibly do another water change later on today. Make sure there is plenty of surface agitation.
In the future for treating ick you might want to use something that is "reef safe" (ie, can treat the whole tank) or get yourself a 10 gallon tank to treat fish separately.
Good luck!!
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