She had come down with hexamita. I think there were symptoms I could have caught early on but I'm new to this and didn't realize she was sick until she stopped eating and retreated to the corner of the tank with her face down in the sand. She slowly began to waste away and though I attempted to treat it with metronidazole, I think the disease was too far along at that point. I got up this morning and could see that she was really beginning to suffer, which I cannot bear to watch.

I mixed 1 tsp each of finquel and baking soda and added that to about 1 gallon of tank water in a fish bowl. I told her I was sorry and put her in the solution. To anyone worried about euthanizing a dear fish, this is definitely a very humane way to do it. She was completely unconscious within about 30 seconds (she was only about 3 in./7.5 cm). 15 minutes after her last breath, I declared her gone.

Ensign Shiny Sides, gone but not forgotten.

I am very sorry to hear this. However, I think you did the right thing, it would be unfair to let the fish suffer.

hard choice,it take a good fish keeper to make a tough decision like that, like i stated before , but seeing an animal suffer is heartbreaking and unbearable.
Good luck with your other fish, chin up!

Thanks for the replies. I had been agonizing for days, but this morning, she just looked so miserable that the choice became an obvious one. My other fish, Flecktarn, is thriving, and at least he now has a 90g tank all to himself. He's only about 5 in./12.5cm at the moment, but I get the feeling he's going to be a beast.

welcome to the monster club lol and im sorry to hear about your loss good luck

So sorry about this... I know it is a hard choice to make.. Chin up and good luck with the other!