Things You'll Need
Small plastic container, enough to hold a gallon of water
Clove oil can be toxic - keep it out of reach of children and away from pets. Properly bury the sick fish someplace where it cannot be dug up - the clove oil is dangerous to other animals if consumed.
Be patient in between doses and be sure to wait the proper amount of time before adding more clove oil.
Many people believe that the best way to kill a sick fish is to flush it down the toilet. This method is ineffective and inhumane. By following these easy steps you can easily kill a sick fish in a humane and loving way.
The first thing you must figure out is when it is necessary to kill a sick fish. If you have a sick fish that is lying on the gravel unable to move for more than 24 hours it is likely a good idea to euthanize it. If the fish has labored breathing or some other condition that it will not be able to recover from you may want to consider this humane way to kill a sick fish. Once you have decided to kill the sick fish you must gather your materials as quickly as possible.
Fill the plastic container with room temperature water and place the sick fish into it using the net or your hand if the sick fish allows you to pick it up without much stress. In a separate smaller container add three or four drops of full strength clove oil to about a pint of water and mix. This mixture will be the initial dose that will start the process that will kill the sick fish. Clove oil can be found at health food stores or pharmacies and costs about six dollars for the purest kind. One bottle will likely last you a lifetime since you will hopefully not have the need to kill a sick fish often.
Pour the clove oil and water mixture into the tank with the sick fish. After about thirty minutes the clove oil will slow down the fish's breathing and put it into a "sleep" state. At this point you can then add three or four more drops of clove oil directly into the tank that holds the sick fish. It will not kill the sick fish immediately but will instead continue to slow it down.
Thirty minutes later add the final three or four drops of clove oil to the water with the sick fish in it. This last addition will eventually kill the sick fish but it will take anywhere up to an hour. The sick fish will slowly stop breathing and pass away peacefully and painlessly.