Wow, thats a good LFS for ya!
Neontetrafan, if treatment is not possible, some people use the freezer method or a swift blow to the head. I have also read that alka seltzer is used. (can anyone verify that?) i think which methods used to euthanize humanely may be a matter of opinion though. i personally have never tried these and have only heard of them,so good luck in what you decide for your fish.
OK HERE IS WHAT YOU DO
Cut the head off then hit it with a hammer.
After that, put it in a blender mixed with vodka and clove oil.
Turn on blender.
Take the blender off the counter and put it in the freezer.
Freeze for two days.
Take it out of freezer and place in a bag and hit it over the counter.
Dispose of in trash.