dc wrote:
Another is to use carbon dioxide fizz tabs-or any other method of
administering CO2 to the water. Place the fish in a small volume of water
in a sealed container with as many as these tabs as you can and the fish
will pass out and die shortly there after.

My fish veterinarian told me once that these tablets induce huge pH
swings very quickly, causing pain to the fish before they die. Far
kinder, he said, to use clove oil. Which is what I have used since. I
used to use those stomach tablets and found it disturbing the length of
time they struggled and gasped for.

Nikki