I shouldn't be allowed to own fish. I wouldn't even have fish except my mother insisted that I get a tank so that my daughter could experience the soothing floaty action. I clean our tank when you can't see the fish any more. Today, it had again reached the point where I wasn't sure if the fish were alive or dead. I cleaned the tank thoroughly and dumped the fish back inside. (Neither fish are named, a testament to how unattached everyone is to the fish - even the bat that terrorized our household last week got named "Alexander".) Not too long after, I clearly saw them floating at the top of the tank. One would assume that the fish would have died in the putrid sewage they were swimming in previously. Instead, they choose to die when they can actually breathe and see the world. Maybe they were shocked by how my oxygen their gills pumped, or by seeing our cat Rex for the first time. (They don't even know that he's less frightening now that his herpes is under control.)
Now that I've cleaned the tank, I'm considering getting another fish. I've gone to all that trouble - it seems a shame to waste a clean tank. If I did, I would get a gold fish, which I could dump in our pond outside when I tired of it. The last time we did that, Halle actually caught "Black Betty" in the pond, flipped her on the bank, and discovered that fish can't survive out of water. Again, too much oxygen can kill a fish.
At least the fish chose a good time of year to die. They will be excellent fertilizer for a really tiny plant.