UPDATE: After adding medication as directed, I dropped in a sinking algae flake (size of a nickel) for my catfish and suddenly the Oscar went after it like crazy! He tried to eat it like 4 times but just couldn't get it down, finally spit it out a fourth time and left it alone. This gave me some hope though, he hasn't even looked at food for 3 weeks now. Could it be he just needs some more exciting food to get back into eating? Live food perhaps?