I need to know what I did wrong

My fish have developed the early stages of Ich and I caught it in time. I walked to the local Walmart and purchased the internet's most recommended remedy, "Quick Cure". I have a 35 gallon (long) aquarium that houses a baby Albino Tiger Oscar, 2 Clown Botias, a Red-tailed Shark, a youg red-belly Pacu, 3 female Pearl Gouramis and a marble Sailfin Pleco. After the treatment of exactly 35 drops of Quick Cure (1 drop per gallon as instructed), my fish were feeling fine and are being very active. Even the botias, who usually hide under rocks until night time, are out and about. It's been about 2 hours since the first treatment and all the fish are doing fine, except my Oscar. He's usually the most active and spends most of the day begging for food and is very loving- he lets me pet him-. But after treatment, he's been lying on his side and moping around.

How can I make him feel better? Or is this just a thing that happens? I have kept oscars in the past and have never experieced them lying on their sides and not moving, even when I remove them from the tank to clean it. He's a B-grade oscar that I saved from just being tossed out because no one would buy him as he was born with a dead eye. Here's a link to his picture http://i.imgur.com/nZmnXiJ.jpg (taken about a week ago)

I'm just really worried about him :c Any advice would be appreciated.