The correct use and the misuse of salt What is salt? Occurring naturally as the mineral halite and comprised of the elements, sodium and chloride, from which its chemical name derives, common salt is also known as NaCl.  Salt is mined from deposits found around the world in large crystalline formations.  These are the result of evaporation from the salt lakes that are former sea beds full of accumulated salt.  Sodium chloride crystals are cubic in shape when observed microscopically although, once mined and put through various processes, salt becomes pelleted, granular, or fine grained depending on its intended use. How safe is salt? Salt has become a multipurpose substance and the raw material has to be prepared for numerous applications.  The purification of raw salt removes impurities such as calcium and also improves its shelf life. This is a bonus for fish keepers as chlorides comprised of calcium, magnesium, and potassium are generally more toxic to fresh water fish species than sodium chloride is.  For over 50 years it has been permissible to include various anti-caking agents with some salt products to keep them free flowing and in some brands, substances to promote human health such as potassium iodide are added. The wisdom of such additives to a basic commodity with so many potential uses, fuels much debate on their safety, particularly in the food industry. Sodium hexacyanoferrate is a common ingredient in salt on sale in the UK and used in aquaculture.  Although this contains extremely low traces of toxic substances there have been no adverse reactions in koi when it is used appropriately.  Pure vacuum dried or PVD salt is safe and inexpensive for koi use and cooking salt can also be used.  There are several products on sale labelled as a tonic or health salts suggesting they are not purely salt based.  I would need to look at all these products comparatively in my laboratory to comment on them.  In this article, all references are to PVD salt and it is this type of salt that is recommended for medicinal purposes in koi. Salt and Koi Every fish species possesses its own unique physiology and highly individual requirements when it comes to environmental salinity as salt has a vital role in normal physiological function. Some marine and tropical fish species need a specific level of salt in their environment to maintain good health, however, koi have no such requirement and should not live in saline water.  It is for this reason that the use of salt in koi keeping should be limited to therapeutic and medical purposes only. Salt has beneficial properties in the treatment of only some koi health problems and it also has the potential to kill all living things if used inappropriately. The main effect of life in saline water is the control it exerts over osmosis. Osmoregulation is the control of body fluids and in koi, being a freshwater fish species there is a higher salt concentration in the body so the kidneys work efficiently and excrete more urine than marine fish species. Total salt loss is prevented by special cells that reabsorb it from urine before excretion. The kidneys are principally involved with filtering impurities from the blood and, when they fail to function normally, fluids are stored in the body rather than excreted.  The mechanisms that initiate fluid retention are complex and a body system malfunction, hormonal influences, and various diseases are all possible reasons. As the underlying cause is rarely obvious it follows that curing fluid retention may not be straightforward. Caution with salt There are many dose levels suggested for dips, baths, and the longer term use of salt. This is confusing so I am not going to add to this with a dose level for a dip.in this article.  Exposing koi to high levels of salt for a few seconds is a risk and even mild dips are stressful to koi. Dips do not have a high level of success as they are often seen as a cure all treatment yet they have no effect internally and are primarily used to lower serious parasite infections on the body or in the gills.  A salt bath lasts several minutes and can be appropriate for injuries, gill infections and thick mucus which is safer than a dip although still stressful.  Long term baths can last for several weeks and are of greater benefit internally depending on the problem. Combining salt with pond medications can create a toxic chemical cocktail so check before using any product in saline water.  If making up a sedative solution, do not use water from a pond or hospital tank that contains salt. Why is salt frequently recommended? With so much advice to use salt in circulation koi keepers could question how safe it is.  This article outlines that salt is beneficial in short term applications. It is the advice to keep koi ponds saline in the long term that should not be acted on.  Salt can help to prevent certain health problems and it also limits the growth of blanket weed which is why it is recommended. However, those who advocate the continuous us of salt have not seen the consequences and are unaware of koi biology.  Koi physiology supports life in freshwater. Saline pond water is far from ideal for life long well-being. Hobbyists are often advised to dip newly purchased koi in a strong salt solution instead of quarantining them. No dip can possibly replace quarantine as the principles underlying both practices are extremely different. Dipping koi in any substance will cause stress and might remove the protective mucus layer. Being stressed and without any mucus, the new koi will become the most vulnerable fish in the pond.  A dip is only likely to help an obvious external problem or a fish that is unresponsive.  Koi are freshwater fish and the use of salt in koi keeping should be limited to the diseases and conditions in which it is known to be of benefit when used at an appropriate level. Salt in the pond Hobbyists often follow the advice to sprinkle a handful of salt in their ponds every week and some keep their koi in far larger concentrations.  Koi keepers do not question such practices, as salt is seen as natural. However, often the volume of salt suggested, such as a handful, falls short of a level that would have any effect if there was a fish health problem.  In other cases, koi are living in too much salt for good health and their long term well-being is at risk.  Whilst some hobbyists favour adding salt to the pond for winter, this practice is intended for koi in shallow ponds of 2 foot (600 mm) deep or fish that were not in good health as winter began.  If koi are struggling in a long cold winter, salt can help at no more than ½ an ounce per Imperial gallon or 0.3% (see table below for metric or US measures).  However, in a well-designed pond with good depth, most koi should not need the support of salt to over winter safely. Salt for koi health How to use salt effectively in the treatment of koi is often misunderstood.  The Internet cannot provide information on every aspect of koi welfare or health as some are highly specialised fields. Articles can become outdated and despite good intentions, some advice is, in reality, perpetuating myths. Advising another hobbyist to use salt when his fish are listless could have consequences if the koi keeper asking for help is unaware his pond has been contaminated so caution when helping others is needed.  Salt cannot cure all diseases or totally eradicate parasites. It is more realistic to state that, at an appropriate level, it can slow down the reproductive capacity of many koi pathogens such as parasites, bacteria, viruses, and other pond life.  It can also help to take the pressure off the major organs during certain diseases. The short term use of salt as an external treatment If a salt bath is recommended then 3–4 ounces per Imperial gallon (approx. 1.9%-2.5% - (see table below for metric or US measures) is the general dose level for a 5 to 10 minute bath.  An airline in the bath makes it safer and more beneficial.  Never leave a fish unattended and, if constant thrashing occurs, discontinue and try again when the fish is calmer.  The term “off colour” could have been created for koi whose skin becomes dull and lacks lustre, or those koi behaving abnormally for any reason. In addition, open skin lesions such as ulcers or injuries will be cleaned by the properties of salt. Gill problems vary as to the cause and some may be eased by a salt bath particularly when excess mucus is coating the gill filaments.  Some parasites such as costia may succumb during a salt bath rather than a dip. The fish leech Piscicola Geometra lessens its hold on a host fish when immersed in salt and becomes easier to remove and the puncture mark made by the leech is bathed to prevent secondary infection. The longer term use of salt as a medicinal treatment The major influence of salt on koi is internal as it will promote the excretion rather than storage of unwanted body fluids which can occur during disease.  In order to exert this control over osmoregulation koi have to be living in salt at 0.3% which equates to ½ ounce of salt per Imperial gallon.  This helps to equalise the blood saline level with the outer environment and any unwanted fluids should then be excreted. The use of salt at a level lower than this will not have the required result and neither will dips or baths.  When there is a serious health problem koi do need to live in saline conditions.  It depends on the disease and the health status of the fish as to how long this isolation in salt should last although several days is normal. Increasing the level of salt to 1 ounce per Imperial gallon or 0.6% (see table below for metric or US measures) can be tried if there is little improvement.  It is better to allow at least 12 hours at the lower salt level before increasing it so it takes effect gradually. The fluid balance and salt The kidneys are principally involved with filtering impurities from the blood and when they fail to function normally fluids are stored in the body rather than excreted.  The mechanisms that initiate fluid retention are complex and can be caused by a malfunction in a body system, hormonal influences as well as disease.  As the underlying cause is rarely obvious, it follows that curing the problem is not straightforward.  Some koi are more prone than others to develop fluid retention and it is more common in spring. Dropsy is not a disease; it is a sign of fluid retention and it can be observed during various diseases particularly bacterial infection. Commonly, dropsy causes the scales to rise all over the body giving it a pine cone effect and the eyes can also protrude. Koi with dropsy, irrespective of the underlying cause, should improve if placed in a hospital tank with ½ an ounce of salt Imperial gallon or 0.3%. After 12 hours, this can be increase to 1 ounce or 0.6% until the bloating diminishes. Once the body normalises in appearance, if bacterial disease is suspected as the cause of the dropsy, antibiotics may be required.  (See table below for metric or US measures). Koi with any open skin lesion can also be hospitalised and treated in the same way as fish with dropsy.  It is vital to balance out the loss of body fluid or the ingress of pond water into the body from any type of open skin lesion and salt can help with this.  Any period of isolation has to be carried out in a well filtered tank as the ammonia level is bound to rise and in cases of dropsy additional excretion is occurring.  Dissolved oxygen levels are very important in the treatment of all sick fish, particularly those suffering from dropsy, injuries, or under any type of medication. The balancing act Potassium and sodium are naturally present in the bodies of fish, being vital components in homeostasis which is the perfect balance of the body, yet there are numerous influences on the levels of these two important substances. Fish depend for their survival on their ability to adapt quickly and cope for short periods in less than ideal water conditions.  For example, freshwater fish such as koi normally live in water with a high level of hydrogen ions. If the pond water suddenly becomes more alkaline, the koi have to produce hormones to cope with this change. The hormones have to create a balance between the new level of alkalinity in the pond water and the internal body systems that must work in harmony to keep the koi alive and healthy.  The organs and systems that make up the body have to process each minute environmental change that takes place and one organ or body system then influences another.  The small behavioural changes in koi all have trigger factors but most will pass unnoticed by the koi keeper who observes only when a major change takes place.  The introduction of salt will trigger yet another phase of adaptation that healthy koi do not need and this is why salt should only be used as a medicine.