Salt and no vinegar

     An overview on salt ,sodium chloride, by Duncan Griffiths 

Many koi keepers have accepted salt in the koi pond system as therapeutic and have used it on a day-to-day basis for many years.

Salt is known to be a strong bactericide and is used in many medical conditions both in human health care and in small and large animal vet practices.

In the koi hobby it is used as a prophylactic long-term additive to the koi's closed circuit environment.

 It is believed that in maintaining a constant low-level dose of salt helps with stress in the fish, maintains a good immune system (stimulating mucus production), and keeps bacteria both Aeromonas and Pseudomonas, to small numbers. It also is believed to help keep ectoparasites low in numbers and finally helps a koi dealing with toxicity from high or constant nitrite levels or other chemical imbalances either internal or external.

Whilst some of the above points may be true some are not, and even some that do have some basis of fact, There can however be equally logical reasons which make the case in the opposite direction


It 's a proven fact that salt does help with stress in koi; in the short term it's very successful for this purpose. So one could draw the conclusion that it is no bad idea to keep koi in a permanent low-level long-term solution. This is not however the case.

The koi should not be subject to permanent long-term stress. This tactic just glosses over a basic inadequacy in the koi keepers system, either poor husbandry or poor and inadequate filtration.

In the short term this is an appropriate course of action, above five to six weeks it is not.

A low-level concentration of salt in the long-term will not protect the koi from a constant barrage of stress the koi will in the end succumb.

But however if the koi's habitat has excellent water quality there is no need for the salt being in place.


The koi's immune system is a very complex mechanism.  The koi’s first line of defense from external threats is the mucus layer of the cuticle, which is produced by the gills and by goblet cells located in the epidermis.

The cuticle contains antibodies, which help the koi defend against disease

Also contained in the cuticle is unwanted debris from the cells of the fish, which is what parasites find so irresistible.

So one could argue if we could stimulate the koi to over produce mucus we could increase its immune system.

The trouble with this theory is, there has to be a greater understanding as to what circumstances cause the over production of mucus.

The koi can over produce mucus for a variety of reasons but to demonstrate the point we will take parasitic involvement.

When parasites invade, it causes immense irritation to the koi.  If on the first few attempts to be rid of this irritation the fish is not successful the koi will begin to over produce mucus. This is an involuntary action on the part of the koi.

If the parasitic condition does not resolve itself, which of course it may not, without medication, the koi will continue to over produce mucus. The next step is the koi gets covered in the familiar slime disease, but by now the koi 's immune system is going into reverse. Why? 

There comes a point in the koi's battle against the irritation whilst it is over producing mucus that the gill lamella gets clogged in its own mucus as a direct result of the excessive production. This in turn impedes the koi's ability to take in an adequate oxygen supply, the knock on effect of this is the koi gets deprived of oxygen by its own making. When the koi's oxygen level drops the immune system begins to degrade.

Its ability to fight the parasite diminishes and the parasite takes this opportunity to over run the fish. The fish then gets weaker and weaker until in the end it simply gives in and dies. Salt in a koi pond is an irritation to the koi, which is why it causes over production of mucus and this is the desired effect and reasoning for its continual use. If a parasite is present without suitable medication to cure the parasitic irritation the salt can make a bad situation worst.

I have on occasion found salt to be the one last piece of the jigsaw that pushed an already sick fish over the edge by further encouraging over production of mucus,  that in turn impedes the fish's ability to respire, plus, salt already depletes oxygen, not by much but it is another factor in the koi's inability to take up adequate oxygen. These factors all come together to finish the fish.

So you can see from this, to subject a koi to long-term exposure to salt is in itself causing it long-term irritation and therefore a form of long-term suffering.

That’s the price of adding salt to get a*good* mucus layer and *immune* system. Having said all that salt as a treatment for koi is usually more of a benefit.

The type of draw back I have just indicated of salt pushing a sick fish over the edge is rare but does happen on occasion.

And it’s a valid point that is worth bearing in mind when contemplating the long-term use of salt.


The case for lowering bacteria is a complex one and is open to many interpretations. Many people say you cant have a completely bacteria free system for many reasons, this reminds me of a strain of bacteria that learnt to survive deep on the sea bed around hot springs gushing up sulphur from volcano's under the sea bed .

  1. In an ideal world even if the bacteria count in the water is nil there will always be bacteria on the fish
  2. The fish will always be producing bacteria in there waste product
  3. You have air bourn contamination including bird droppings etc
  4. Bacteria from plants in the pond the list could be endless.

It’s a recognized fact that salt does kill bacteria, what types and how many, will be the topic of many a hot debate. If you buy into the fact that salt kills bacteria, you also have to buy into the fact that to keep salt in the pond on a permanent basis there must be no half way measure's, that salt either kills or it does not. (Salt kills all or salt kills nothing) if your uncertain what strains are left and how many what was the point?

            I know the advanced hobbyist will make it his mission in life to find the answer to this question, but the everyday hobbyist will probably never know. He will simply keep adding salt thinking this is an appropriate course of action rightly or wrongly based on what he has observed some other folks in the hobby do.

A simplistic view true enough, but if you accept the last few statements you could argue the fact it might not be possible to lower the bacterial count with salt alone

BUT again it's not quite that simple.

I am reminded of a saying, "Man rules the earth" some say it’s the “insect” others “mammals”.

Make no mistake this planet belongs to Bacteria!

The bacterial evolutionary trail is impressive to say the least.

Bacteria evolve to changes in its environment faster than any other organism, the evolution time scale for bacteria when it is forced to adapt to change is measured in a year or two probably less, not hundreds and thousands of years as it is with the animal kingdom.

We share this planet with bacteria not because bacteria allow us; no matter how effective bacteria are at the survival game our immune system is far better in most cases.

I say most cases because we still have to live with bacterial strains that are ever present and are a very real threat to humans and animals and our immune systems have not yet learned to combat such strains.

So it seems that bacteria are better able to adapt in evolutionary terms than we are

With this in mind you will have to assume that there will be bacteria in the pond system for which salt poses no threat. And for the strains that are effected to constant levels of salinity and do succumb readily, these strains did not magically appear in the pond system and are likely supplied to the pond from readily available sources on a continual basis.

And upon entering the system and continually meeting an opponent like salt, they should eventually adapt, and ultimately over come the very thing you put in place to stop them.

 If bacteria can overcome antibiotics, bacteria can and should reign over salt.


Salt has been used for eradication and control of parasites, well longer than I care to remember, and it does seem by many to be very effective for this purpose. Although personally speaking I have yet to find a case of parasitic outbreak that salt has cured for ME.

But then again the author is known for taking a more direct approach to parasitic outbreaks thanks to Mr. potassium permanganate and Mr. Chloramine T

When using salt for parasitic control the salt acts like a piece of blotting paper soaking up water, this process is called osmosis.

Osmosis and osmotic shock



A term for the transfer of a fluid through a membrane from a low to a higher concentration solution.

In ordinary circumstances in a fresh water system when salt is added to the system lets say 0.6% salinity any fresh water of nil or low salinity migrates to the higher salinity until the concentration equalizes 

However  on occasion this appears to work in the koi keeper's favor for a couple of reasons one of which will be discussed in the very next section.

But from the parasitic point of view, as salinity is increased in the koi pond the fluid in the body of the parasite being of a lower value to the outside salinity begins to migrate to the out side of its cell walls in an effort to equalize the pressure difference.

Thus dehydrating (crenates) the parasite, and destroying it.

The object of the game in this instance is to increase the salinity very quickly, in fact as fast as the koi can withstand. So as to create an unequal concentration between the inside body fluid of the parasite, and the surrounding water. The cell cannot adjust in time to stop the loss of body fluids.

The same is also true of saltwater fish and its parasites but in reverse.

If you dip a saltwater species' suffering from parasites in fresh water the fresh water migrates into the cell of the parasite, as the fluids of the parasite is of a higher salinity, and  as the parasite inflates with fluid its cell wall is breached.

So you could say the fresh water parasite implodes and the saltwater parasite explodes. So from this you will observe that the key to parasite control is to move upward in salinity as quick as is safe for the koi.

If the occasion arise to increase salinity slowly which is often the case with low  permanent  maintenance salt doses the effect is lost. The protozoan has time to adjust (exchanging its body fluid for one of a higher salinity).

Additionally the concentration difference is a lot less in a lower salinity, so a lot less osmosis takes place.

I have personally seen flukes, trichodina and costia living quite happy and oblivious to the fact that their environment was 0.9% salinity            

The koi does not suffer from these adverse effects of salt osmosis because of its complex osmoregulatory system, which sets up a defense against the exchange of fluids

But there are circumstances in koi where this system fails and that is the subject of further sections.



The koi has a very complex system for the exchange of salts, body fluids, the intake of minerals, which it constantly exchanges and processes,

The process that controls all this is called the osmoregulatory system.

Because the koi's body fluid is of a low salinity and its natural surroundings even lower or nil in terms of salinity, there is an obvious saline concentration difference. Water moves into the koi via the delicate gill lamella membrane and membrane of the gut. Also salt ions migrate out of the koi by diffusion via the gill lamella. There is a continual complex exchange of salts and fluids in order that the koi strikes a very difficult and even balance.  The koi's kidney is super efficient and replaces lost salts by reprocessing and reabsorbing salt from urine and trace salt in the pond system. The koi is also balancing its own pH in the blood stream. The gill will exchange hydrogen and bicarbonate ions in exchange for sodium and chloride ions, in order to take up and renew lost and utilized salts from its surroundings and stop its blood pH from dropping by the accumulation of bicarbonate and hydrogen ions. This may be an explanation of why people say a high pH is not good for koi It might be the case that the koi cannot dump hydrogen and bicarbonate ions into an already saturated system with high pH

This is a very brief look at osmoregulation it will be touched on in later subjects.




As already stated the koi lives with osmosis every day, it's a natural occurrence in the day-to-day life of a koi. But there are a couple of instances when it becomes unnatural, and when this results its called “Osmotic Shock” and can and will result in fish death.

Take an every day koi swimming in an everyday pond none saline (typical salinity of tap water 0.05% or lower) so this could be classed as a typical, none or very low salinity pond environment.

As previously mentioned The koi lives with a natural osmosis taking water on board into the blood stream and tissue extracting natural elements as it goes about it's business.After the kidney has finished processing these elements, this fluid it is excreted mainly via the gill (ammonia), much as animals and humans excrete waste body fluid.

The reason for this is the koi's body fluid is 0.9% salinity or = to, 1.5 oz per imp gallon salt.  To put it into terms easier to understand, the fresh surrounding water try’s to equalize the concentrations from low to high (external to internal) or you could say the koi's higher concentration body fluids draws the fresh water into the body to equalize the concentration. Also because the body is 0.9% saline the salt migrates out of the koi to a non-saline environment (diffusion), so the koi is continually losing body salts and exchanging fluids

This is a continual process 24 hours per day, and again an involuntary action.




However if the fish has an open wound or a deep ulcer, this provides an uncontrolled entry point for the water to ingress to accomplish the equalization process, the fish has no control over this event should it arise the koi's osmoregulation system has to try to cope.


The rapid induction of water into the koi's tissue and blood stream means that the koi's kidney has a very heavy load placed upon it, as it now has to process excess and waste fluids. Eventually the kidney's function is impaired, and the influx of water can't be coped with. Then the fish begins to bloat and swell with bulging eyes (dropsy)

However if you raise the salt concentration in the environment (water), you reduce the amount of water entering the fish which unloads the kidneys.  At a water concentration of 0.9%, the inflow of water thru the ‘hole’ is greatly reduced. You are equalizing the concentrations internal and external to the fish thus decreasing the amount of water entering the body (less osmosis taking place) giving the fish time to heal and close the portal of entry for the water (the ulcer or damage).

There is another situation in which osmosis takes place in koi which does not require an additional entry point, and that’s bacterial or viral dropsy.

When a viral or bacterial infection compromises the major organs and kidney, and either impairs the kidneys function, or shuts it down. This stops the koi from ridding itself of excess waste fluid

In the case of virus there is little that can be done, as there is no recorded and confirmed cure for virus.

But for bacterial infection however there is. The koi should be supported with either antibiotics and salt or proflavine hemesulphate. And salt at 1.0%

This therapeutic hypertonic dose of salt draws the excess fluid back out from the fish, whilst the antibiotic or proflavine sets to work on the infection to get the kidney functioning again if not to much damage has already been done.

With these two conditions salt is indeed the weapon of choice with what ever topical remedy works for you.


When a koi is in stress it will lose body salts.

Ordinarily this is a normal event, but because the koi is stressed its kidney will not replace salt by process from its normal sources.

From all the above it is also easy to see why salt used as a stress aid does work.

As a slightly hypotonic salt solution in the pond water will greatly reduce the koi from loosing salts, and stops the osmotic effect on fluid induction.


1. A salt solution equal to the koi's own saline concentration is said to be isotonic

2. A salt solution greater than the koi's saline concentration is said to be hypertonic

3. A salt solution less than the koi's saline concentration is said to be hypotonic.





When a filtration system breaks down and toxins are not processed as would normally be the case, or a new virgin filter is being cycled, We can normally expect to experience high ammonia or nitrite levels.

This will soon have a negative effect on the koi if left unchecked.

As these levels take up to 6 weeks to subside, we then have to consider other ways to help the fish deal with these toxins in order that the koi survives, and salt can go a long way to this end.

A well-salted pond protects the koi in a few ways.

First off when dealing with high ammonia salt helps the koi over produce mucus, and this offers protection in the short term from, ammonia irritation and ammonia burns.

I say short term because ammonia normally subsides in about ten days or so.

By then the nitrite is on the way up to dangerous levels and this will take the rest of the afore mentioned time span to abate.

Nitrite toxicity affects the koi by altering the hemoglobin in the koi's bloodstream, affecting its capacity to carry oxygen.

If a koi hemorrhages whilst suffering the effects of nitrite toxicity it will be noticed that its blood will be brown instead of bright red (brown blood disease).

Salt helps with this condition because the Chloride anion competes with the nitrite anion for entry into the gill lamella, thus alleviating some or most of the toxic effects.

Plus it will also help the koi deal with the stress and fluid loss whilst dealing with this dilemma.




Upon introduction of salt into a filtered system many people say that salt does not affect the helpful bacteria in the media. This is both true and untrue to a curtain extent.

A salt solution of 3.0% will destroy all filter bacteria but we do not use these concentrations in the koi pond

Salt added at 0.3% or 0.6% or 0.9% or even 1.0% although perceived to be of no effect to filtration bacteria will in fact destroy curtain types of bacteria in the filter.

But equally there are types of bacteria in the filter that salt at these levels will not affect, and these will pull in the slack.

As long as the salt is added slow enough.

As with all things in life there is no gain without some pain.




It has been documented that constant exposure to low-level salt will dull out the colour in koi by acting on the pigment cells called chromatophores found in the dermis




Short-term treatments

Short-term treatments of salt in the koi pond should be limited to

1.      0.25 oz per imp gallon  (for stress)

2.      0.5 oz per imp gallon   (parasite control or bacterial infections) this also causes the fish to over produce mucus and as a result some parasites get sloughed off with the excess mucus

3.      0.75 oz per imp gallon (parasite control) (not recommended for pond treatments quarantine only)


4.      1.0oz per imp gallon (not recommended for pond treatments quarantine only)

            For bacterial gill infection or dropsy (extra O2 always)

Always make sure the salt is well dissolved and never put the full dose in at once

Divide dose into 4 equal parts and Spread it out 12 hours apart to avoid shock to the koi.

Equally never drop it as quick if anything take it a little slower there is no mad rush, in fact there is a little table at the end of this paper to demonstrate just how hard it is to get out of the system once in there.


Caution here!  Dips are extremely stressful on the koi, as they mostly tend to be of a very high hypertonic concentration.

3 oz per imp gallon for 5 to 10 minutes very effective for cleansing the gill and for parasite eradication and bacterial infection

Warning! If the koi rolls over during this treatment don’t panic but return the fish to the pond immediately, where on it might still stay on its side but be assured it will in half an hour or so start swimming again with no ill effect

There are higher hypertonic doses than this but I do not recommend them although I have practiced them.



There are many do’s and don’ts with salt,

One of which is salt and potassium permanganate should not be mixed.

This is not the case they are perfectly compatible, I have however read of cardiac arrest in koi when these two treatments are mixed, but have not seen or heard of a single case to relate to you here.

But it must be born in mind that each of these two treatments in its there own right depletes oxygen, so extra care is needed.



I have many books that say that these two cannot be mixed and yet nobody gives good reason for this statement. I know many many people that treat with formalin and salt with no ill effect including myself so I am speaking from personal experience, as long as the salt level is below 0.3 oz per imp gallon and extra oxygen is administered during the treatment all should be ok. As formalin is probably the best oxygen stripper there is.

But your heart will be in your mouth the very first time you try it if memory serves




It is said by many that anaesthetic and salt should not be mixed some of this is also not true personally I use benzocaine and have on many occasion used it with salt with no effect either before during or after the anaesthetic. However MS222 should not be used with salt.

But the strange thing here is that MS222 is the water  soluble version of benzocaine,

So go figure.

Oil of cloves I cannot comment on as I have only on rare occasion had to use clove oil, but some experimentation might be called for.

Basically as far as I am aware  there are virtually no mixtures that cannot be achieved whilst using salt, apart from two or three exception listed here that cant be substantiated, but you might want to tread a little careful if you should decide to try these for yourselves.


Now you may have formed the opinion that the author is very anti-salt. You would be very wrong.

I just believe that there is a time and a place for almost everything and everything in its place.

Its true I do not keep koi in salt permanently just because I can, and it  * seems * like the appropriate thing to do.

Koi were born to live in a non-saline environment and only live in saline by human intervention, but if you want to keep them happy and healthy salt is not part of the equation in the long term.

Short term is a very different matter. There are lots of occasions that salt is very appropriate and indeed is the only course of action. Just learn to recognize those moments in time when it is needed. Then go for it.

All I have really tried to do here is lay out some basics and some explanation, as simply as I can so as the not so experienced and newcomer to the hobby can judge for him or herself whether or not and how salt is going to be used.

 Based on a little more data than. “My mate uses it and swears by it”

 I have tried to explained the why’s and the when’s and the why not’s, so as we can make an informed choice as to whether or not to use salt and how to.

And ultimately that choice is always going to be yours not the koi’s.


For those of you that can and will use salt and think it’s a piece of cake to get out of the system with a couple of partial water changes once in there.

 This last section on the following pages is just for you


Thank you for taking the time to reading this my first koi paper


Check out how difficult it is to be rid of salt once in the sytem click here