I had two pictus cats about 21/2 inches each. They were shy but otherwise fine for months. I brought two more home and everything seemed fine that night and the next morning but later that day I found the two new ones dead and the two old ones sick. Panting and floating straight up from the bottom. I quarentined them and tested my tank. All my levels were 0. And all myy other fish are acting kind of weird hiding in the corner in groups like they are afraid. I don't know what could have happened.