Prevention is the most important thing, because prevention is much more easier than cure your koi fish.

You need to prepare yourself for the time, when your koi fish will be sick. First of all you need to know a bit about the different fish diseases. One of the principal causes of fish mortality is bacterial disease. I suggest you to read some articles or books about koi fish disease. For example: "The Manual of Fish Health" from Tetra Press, "Koi Herpes Virus, The Deadly Disease" or "Little Koi Disease Guide" from me.

I suggest you to make a koi first aid kit, which will contain the following supplies:

PH test kit for measuring the pH level of your pond or aquarium water.

Ammonia test kit determines the level of toxic ammonia, which can come from fish waste and urine, uneaten fish food and decaying plants or dead insects.

Chlorine test kit which rapidly treats fungal infections on body and fins of pond fish. Also treats internal and external bacterial infections.

De-chlor: this water conditioner instantly eliminates chlorine and reduces toxicity of common heavy metals.

Dylox used to control anchor worms (Lernea), gill flukes (Gyrodactylus and Cleidodiscus), and fish lice (Ergasilus and Argulus).

Malachite green is effective against certain protozoan parasites and fungus infections of fish and eggs.

Betadine is an iodine compound used to disinfect eggs against bacterial infections and possibly viruses.

Methylene blue is effective against ectoparasitic and fungal infections.

Salt most useful chemicals in the treatment of external diseases of fish.

Formalin is one of the most often used chemicals in the treatment of external parasites of fish.

With the help of these medications you will be able to cure your koi fish.