RXP is not an effective treatment IMO.
Is the fish eating? Is there enough oxygen in the tank - I don't think a blanket on the tank will help gas exchange.
Might be too late for that specimen - many are improperly caught or handled
I'd make sure there's enough flow in his tank, treat with Cupramine if it's ich... what symptoms does he present with? If it's breathing heavy, look closely at its eyes - if it has cloudy eyes it could be trematodes or flatworms - they infest the eyes, gills and mouth. A 7 minute freshwater dip should offer it some relief. Copper will not kill trematodes but PraziPro (or other praziquantel medication will help).
HTH
Jenn
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