|Salt is an irritant to the skin of the koi. As a reaction to the irritant the koi will grow additional slime coat. The slime coat is the first line of defense against bacteria and parasites. It is in this way salt is a useful tool in koi keeping.
Salt definitely has it's time and place in koi keeping. It can be very useful in treating stressed, sick and new koi and it can also be great at controlling parasites. However it is NOT a good idea to leave salt in your koi pond all year long. There are no real health concerns from long term salt use in a koi pond, but the problem occurs with parasites. If salt is used year round, parasites can build up a resistance to salt and you end up with these super bugs. Then you will have a much harder time later trying to kill off parasites and even more drastic measures have to be taken. Such drastic measures can often times be dangerous to the koi. So use salt sparingly and remove the salt with water changes once you are done. Remember, salt never dissipates, only water changes can remove it.
If you want to use salt, there are several times I do suggest it.
First, salt as a mild tonic....
Short term use in the Spring can be helpful. The immune system of the koi is weak from the winter and adding salt can help them grow additional slime coat to protect them from the parasites and bacteria. The bacteria and parasites become active weeks, if not months, before the koi and filter are working at full strength. This time is known as "Aeromonas Alley". Adding salt can help protect the koi during this vulnerable time.
Another time is when the koi are stressed for any reason. Red veins, clamped fins and lethargic behavior are signs of stress. Many times a low does of salt can help buy some time until you figure out what the problem is. Stress can occur for a wide variety of reasons, water quality, changes in water parameters, internal infections and parasites just to name a few. Adding a low dosage of salt probably won't resolve the problem, but rather help the koi maintain its natural defense while you hunt for the real problem. Sometimes people add the salt and the koi start to improve, so they consider the problem solved, but as soon as you remove the salt, the problem returns.
Another use for salt is when you have new koi being held in quarantine, they are often stressed from transport and they have shed their slime coat. Adding salt to the holding tank can be very helpful.
For all the situations above the suggested dose of salt is between 1 and 2 pounds of salt per 100 gallons of water. I know, it sounds like a lot of salt, and it is. One pound of salt per 100 gallons will give you .12% salt content. This is a mild tonic to help ease stress and rebuild slime coat.
Second, Salt as a method for killing parasites...
Salt also has uses in parasite control. However this will require much higher doses of salt. Usually in the neighborhood of .5% to .6% salt. This is around 5 pounds per 100 gallons of water. Now that's a lot of salt! You may find some literature out there that says .3% salt will kill parasites, but check the date on that information. 10 years ago .3% salt did kill parasites, however due to its heavy use by breeders, many strains of parasites have developed a resistance to salt. So now much higher levels of salt must be used. I am sure 10 years from now salt will be completely useless at killing parasites, but for now .6% for around 2 weeks will kill many types of parasites. Salt however will not kill flukes, anchor worms or lice. For that other treatments are needed.
A few other things to keep in mind.
1) Salt will kill most plants. You will need to remove any potted or floating plants before adding salt.
2) Salt will never dissipate. If the water level drops from evaporation, the salt will only become more concentrated. The only way to remove salt is to drain water from the koi pond and replace with new water.
3) You can use water softener salt in 40# bags for around $5. Look for a bag that says 99.5% pure salt (or higher).
4) You can use salt to determine the exact number of gallons in the pond. Test the salt level before you add salt. Add a known weight of salt. Then measure the salt level after you add the salt.
We know the 1 pound in 100 gallons will give you .12%. The basic formula is Pounds of salt divided by Change is salt concentration (in Parts Per Thousand which is % times 10) times 120. Or V= (P/C) x 120. So if you add 20 pounds of salt and the salinity went from .05% to .3% the change is salinity is .25% or 2.5 ppt. The formula would be V= (20/2.5) x 120 and V = 960 gallons.
5) I have found the reagent drop salt test kits to be quite inaccurate for most purposes. A digital salinity meter is far superior to reagent tests.
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