Well, he just passed a few minutes ago =( His left fin was pointing straight up. He's been laying on his side the whole day until now. I am not sure what he died of. The tank's condition seems to be fine, as all the other fish and fry are not affected. I tried putting him a quarantine tank with a little salt, but I guess it was just too late =(
P.S. He was my favorite too.

I have a male guppy who's been acting funny for the last 5 days. He was fairly active at the beginning of the week, swimming around and even swimming against the air bubble currents. But gradually during this week he's been more and more inactive. Not swimming around like before, and today he's been laying at the bottom of the tank. The temperature seems fine as all the other fish and fry are doing well. I have also recently did a water change 2 days ago. His fins seem to flop to one side and he seems to be twisting his body as if almost laying on his side. When the other fish pass by sometimes they would peck at him and he would react and swim away quickly. I don't see him eating either. I have researched online about ichs, fin rot, etc, and I don't see any physical symptoms like split fin, or white spots or slime nor anything dangling from his body. All of the other fish are doing fine. Please tell me what I can do to save him if possible. I have a 15 gallon tank and feed him brine pellets - nothing else. Please tell me what I can do. Any help is much appreciated!!!!!