Bastard Fish

We decided it was high-time that the boy have his own pet, so we went with something small. A 5.5 Gallon Tank and two small feeder fish, which were named Dorothy and George. Promptly and within the space of a week, the fish began to die. Red spots appeared on their scales. We got medicine which we administered in the correct doses, and I cleaned the tank on a more than regular basis, removing 25% of the water at a time. Still, they continued to die. Their tails were eaten away. Red spots gave way to white fungus growing off of their fins. Near the end, Dorothy couldn't swim anymore, and hence couldn't eat. I tried extraordinary measure to try and save her, by placing her in a separate bowl with a higher concentration of medicine, and held her in the fish net near the surface to try and feed her, but to no avail. Soon I had to explain to the boy that his fish had, "Left," to which he asked, "Where?" to which I replied, "Away." George meanwhile looked like he could make a recovery, he was swimming, if a bit erratically, and his fungus had cleared up. The next day, it was back, and he was much in the same state as Dorothy. I tried another water change to see if it would help matter, along with additional beneficial chemicals I had not previously used, like Cycle and Waste Control. It died shortly.
After completely washing every inch of the tank and it's ornaments, we went out and got two new fish, slightly larger. One was orange and white, and one was white. After about three hours, I passed by the tank, seeing only the one fish. I tried searching for the other, but reasoned it must be hiding. Another hour later, I come by again, and look more closely this time. The fish is found lying on the floor, quite dead. It had leapt from it's bowl, which is quite the feat considering there's an inch or so between the surface of the water and the edge of the aquarium. So in the space of three weeks, I've lost three fish. In the past, I've had fish which live nine years past their expected life spans, but I guess I don't have the magic anymore.