Sounds like you are doing everything right.
Yeah try 2 5 day treatments but after the first one do a 40% water change and place carbon in the filter for a day then re do the medication,after removing the carbon. This is so you dont overdose the tank Make sure you have plenty of air and water movement in the hospital tank.
Yeah I know how you feel about the oscar, I worry at the slightest mark on mine.
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TONY
Australian and proud of it!! My Cichlidfish.com Home page