Discussion To Salt or not to salt ? – That IS the question

One of the most controversial topics in Koi Keeping

If you are considering using salt in your pond, then please read through this discussion article. We hope it will help you understand the pros and cons of why and how it is used before going ahead.

Pond Salt used to be the go-to solution for killing parasites and protecting koi carp during the winter months, before there was an extensive range of pond treatments on the aquatics market. Today there is a vast spectrum of thinking amongst Koi keepers when it comes to using salt – and opinions are very variable.

Koi are perfectly adapted to living in a freshwater environment. They can tolerate VERY low levels of salt – BUT a healthy Koi does not need additional salt in its pond water to keep it healthy

Adding salt to your pond to create a, higher than normal level of salinity artificially, and maintaining that level will not provide any benefit to a healthy Koi.

In addition, a long-term increased level of salt in a pond environment may provide an opportunity for parasites to develop an immunity to the effects of salt, making it less effective when it’s really needed.

SO – Why Might We Use Salt (Non-iodized salt, Sodium Chloride (NaCl)) in our ponds?

Salt is an inexpensive method used by many Koi keepers over the years, to help

to treat EXTERNAL bacteria and parasites,
to counteract the effects of stress
improve mucous/slime coat production and increase the Koi’s resistance to external infections and infestations
and fight nitrite toxicity,

and which doesn’t have too much of an adverse effect on the biological parts of pond filtration systems.

1. Treatment of EXTERNAL parasites and/or bacteria on a Koi’s body.

Koi live in freshwater. So do many parasites and bacteria. Salt treatment of a koi pond can help eliminate these freshwater parasites and bacteria.

According to Dr. Erik Johnson, one of the authors of “Koi Health and Disease”, Salt at 0.3% is credited with the clearance of the following:

Chilodinella (24-36 hours)
Epistylis (24 hours regardless of temperature)
Ichthyophthirius(72 hours at tropical temperatures)
Costiasis (Ichthyobodo necatrix)
Trichophrya(24 hours regardless of water temp)
Glossatella(24 hours regardless of water temperature)
External Tetrahymena
Almost every single Trichodiniid/Tripartiella organism.

It can also be beneficial by:

Inhibiting trematode reproduction – clears up to 30% of adults.
Inhibiting some types of fluke (Lerneiid) reproduction

However, parasites appear to be becoming more resistant and the salt to be having less of an effect, though it can work well for some bacterial infections such as columnaris.

2. To counteract the effects of stress

When a fish experiences acute stress from injury, disease, handling or transport, their body releases neurotransmitters and hormones into their body tissues. These often have the effect of making the fish breath faster, over-hydrate and to lose salt.

This can in turn, lead to an osmotic imbalance, as a result of ion depletion – the most life-threatening impact of stress.

To counteract this, though some people will say that salt can be used to a level of up to 0.75% and maintained at that level for no more than one week, we would recommend that the level should not exceed 0.6%, before reducing the level gradually with regular water changes.

3. To balance a Koi’s osmoregulation and encourage recovery from sickness

As we’ve said, Koi are freshwater fish. Their bodies do, however, contain some salt, at a level in the body fluid that is (normally) much higher than the surrounding water.

Water passes into their bodies continually via the process of osmosis.Under normal conditions, the koi does not burst because it can regulate its body salinity level and can excrete excess water through its kidneys as urine – thus maintaining the correct balance.

When a Koi gets sick or stressed, this can affect its ability to balance osmotic pressure. To help remedy this, we can add salt to raise the koi pond salt level to more closely, match that of a Koi’s body fluid. This way the water does not enter its body as much or as quickly. The benefit is that the Koi’s body does not have to work as hard to maintain its osmotic balance, which can help it recover quicker.

So at NO MORE THAN 0.75% (and ideally 0.6%) salt can act as a medication, and can do several jobs,

it helps with any osmotic imbalance
act as a bactericide and fungiside
and helps clear the fish of some parasites

AND Salt also stimulates the production of mucus – the Koi’s natural external defence system.

BUT do be aware,

Salt is not so effective against flukes which it suppresses but doesn’t eradicate,

or Costia – which requires an even higher salt concentration, and therefore is not suitable to use in the whole pond.

AND don’t forget – if you use salt in the whole pond you are treating all your koi equally whether they warrant the treatment or not.

Now that you know why salt is used, the next question is, “Should I put salt in my koi pond?”

There are several scenarios when you might decide to use salt. eg

If you have a high nitrite level (High nitrite levels can be toxic to fish. Salt will help make nitrite safe until the filter is working effectively again).
Before introducing a new koi to your pond
When a Koi swims awkwardly or is obviously sick.

In both the second and third situations, it is highly recommended to treat the individual Koi in a quarantine tank rather than in the main pond. (See more detailed section below)

NB Short-term baths in very high concentrations of salt are hugely stressful for a fish. Whilst dipping may kill parasites on the fish, it doesn’t protect the fish against re-infestation once it is introduced/returned to the pond, and it doesn’t necessarily address the root cause of the problem.

In the autumn and winter, some argue that using pond salt will protect the fish and help them to survive the cold winter months.

In winter, it is thought that salt in the pond water can help koi by replacing salt that the fish would naturally produce themselves.

When pond water gets colder, the fish’s metabolism slows down and their organs begin functioning less than they would in warmer water. Using a small amount of salt is thought to help replace the natural salt they would normally produce but are unable to do so, due to this reduction in normal function – the expectation being that it will make the cooler winter temperatures more bearable and survivable for the fish.

To this end some koi-keepers are very much in favour of maintaining a permanent, low, salt level in their ponds – at all times.

We do not agree and believe you should only use salt when it is needed.

So long as the water in the pond stays a few degrees above freezing, then that will be enough to keep koi functioning through the winter.

What Type of Salt should be used for Koi Pond Salt Treatment?

Keeping your pond water at the optimum condition for your Koi is a complex chemical balancing act.

It is important at this stage to consider what level of dissolved salts may already be in your your tap water?

As in Japan, in the UK we have varying levels of water hardness depending on whereabouts in the country the water has come from. Water which contains a relatively large number of dissolved minerals is described as hard, while water with low mineral content is described as soft. This hardness is usually caused predominantly by calcium and magnesium salts – already in the water at measurable levels – whereas in soft water areas there may be none.

Koi do best in a carbonate hardness of 150-300 mg/litre or 9-18 degrees of hardness. In most artificial Koi ponds the water is relatively soft, due in part, to there being no natural mud bottom that leaches minerals into the water.

Adding salt will act to reduce the natural hardness of the water in your pond. As with commercial and domestic water softeners, when you add salt (Sodium Chloride), the calcium and magnesium ions are replaced with sodium or potassium ions. The softening effect is due to the removal of the hard water minerals, which are the calcium and magnesium.

The subject of water hardness is, of course, another keenly debated topic among koi Keepers – and probably best left for a more in-depth discussion at a later date. But, suffice it to say, depending on which koi keeper you ask, some will claim that soft water is better for koi, and others will stand by hard water.

Alongside general hardness, you also have other closely linked water quality parameters, alkalinity (pH), KH (carbonate hardness), and TDS (total dissolved solids) This is where confusion can arise, as not only are they measured in similar ways, but the definitions sometimes overlap depending on the source of the information.

An easy way to check the salinity of any water is with a pH and conductivity meter. Depending on the actual meter, you may be able to convert to total dissolved solids (TDS) or salinity manually or simply use a pH and conductivity meter that has this conversion feature built in.

All of which support the recommendation that each pond should be considered, in its own right, and in isolation. No two ponds will behave in exactly the same way – there are so many possible parameters and variations to take into account.

If you decide to use salt, only ever use non-iodized pure salt.

You can buy a big bag of suitable salt at koi dealers, DIY or hardware stores AND avoid table salt or any iodized salt.

Always use a salinity meter to ensure you are accurate when it comes to measuring the level of salt in your pond water

Salinity meters are an easy-to-use water quality indicating tool and are a great way to obtain a quick estimate of the dissolved salts present in a wide range of water samples.

When looking for a salinity meter, it is important to check whether the units of measurements are suitable for your requirements and choose a device with automatic temperature compensation (ATC) to make measuring faster and easier.

Electrical conductivity is the measure of the concentration of ions present within a sample.

Adding marine salt and sodium bicarbonate increase hardness and so will also cause the pH to rise.

Be very careful when using other, proprietary medications if you have salt in your pond. Read the labels very carefully to ensure that they are safe BEFORE you use them. Some are not safe to use in combination with salt. If you have any doubts please check with the manufacturer.

**AND – do avoid using salt with formalin.**

Salt and formalin do not get along. If you use salt and formalin together, it could kill your Koi.

How Much Salt Should You Use?

NB Salt is toxic to Koi if used at high levels for long periods of time. If you use too much, it will shut down their kidneys, and kidney failure is one of the main reasons people have problems such as “pop-eye” or other symptoms such as Dropsy.

1. Quick Salt Bath Option for Koi Rescue

Some would say this is the best and safest way to use salt, and it is mainly intended to kill any parasites or bacteria on the surface of the body.

It is a quick salt bath (But do be careful!) –

select a bowl large enough to enable you get sufficient water in it to keep the koi submerged
dissolve as much salt as possible into water.
move the Koi to the bowl and leave it there, in the highly concentrated salt water, for a short time.
as soon as the Koi begins to float, and you see a whitish layer developing on the body
rescue the Koi from the bowl and release it back into your pond immediately.

However, this could kill your Koi if done incorrectly.

So, I recommend this method only if you are experienced or are with an experienced person

2. “Whole pond” use

As was mentioned earlier all tap-water in the UK contains a certain amount of dissolved salts. If you decide to go for the whole pond approach to salt use, DO BEAR THIS IN MIND BEFORE ADDING ANY MORE SALT to the pond-water.

There are no standards for hardness in the Water Quality Regulations for the UK, neither are there any health based standards for the hardness of drinking water, as hard water is perfectly safe to drink. There is even a lot of evidence to suggest that hard water is actually good for human health as it can provide many of the natural minerals that your body needs.

Always measure the salt content of your tap water and/or pond water BEFORE adding additional salt – and only add sufficient to bring it up to the required level of total Salt

Treating sick fish

For treating illness ( stress/bacterial problems), the suggested dosage varies from 0.3%–0.6% salt level – depending on the source of the recommendation.

I recommend you start with 0.3% and gradually raise it to 0.5% – but only if you feel it is absolutely necessary.

Levels as high as 0.6% are recommended only when ALL your Koi seems to be very stressed or sick.

In the event that you are using Salt for consistent (semi-permanent) use, for example as prophylaxis to reduce the risk of bacterial infections etc., it is recommended that the level should be much lower – 1 kg (2.2 lb) of salt per 1000 litres (265 gallons) of water, which makes approximately a 0.1% saltwater solution.

In either situation, spread out your salt treatment over a few days and continue monitoring the salinity levels of your pond water.

For the safety of your koi, you SHOULD NOT use too much salt, for too long – it could be deadly!

So long as the situation is not too critical, before you add salt to your pond, remember to do a bit of housekeeping –

clean the pond and filter,
remove any plants,
perform a 50% water change,
and – add the salt all in one go

You should let the salt dissolve in a bucket of pond water before you add it directly to the pond.

Leave it to fully dissolve and then add it all into the pond gradually, spreading it around as much as possible. This helps avoid “burning” your koi with saline that is too concentrated or salt that has not fully dissolved.

If you are using salt to treat parasites – depending on your prevailing water temperature, with salt concentrations of up to 0.6%, it may take 14–21 days to completely treat them effectively,

Remember that salt does not evaporate; and if you do a water change whilst using salt, top up the salt level based on amount of the water replaced, not the total volume of pond.

AND BE CAREFUL – The only way to remove salt once it is in your pond is by doing a series of partial water changes.

Take care not to release the excess water onto a tree or garden plants as the salt could do some damage if they have no tolerance for it.

AND do bear in mind that even 50% water changes will only dilute the salt by half each time. To get it down to very low levels you may need to do quite a number of changes. (effectively if, for example, you start with a salt level 1% above your baseline, it could take at least 5 x 50% water changes to get the level down to where you started – each change effectively reducing the salt by 0.5 +0.25 + 0.125 + 0.0625 + 0.032 = in total 0.97 of the original level

How Do I Check Salt Level in My Koi Pond?

Use a digital meter.

Please never guess your pond’s salt level.

Check the level to establish a baseline before you start, and please check your salt level every time before adding more salt to your pond.

We recommend a Digital Salt Meter – they are far more accurate than a “drop”salt test kit.

Use this digital salt meter before and after salt is added.

Remember, salt is toxic to your koi and you do NOT want to add more than is recommended, or you will risk losing your koi.

And when calculating – be really careful about the decimal point. The difference between 0.03 % and 0.3 % could mean using 10 times too much or too little.

Will Adding Salt Kill Pond Plants?

Despite the fact that aquatic plants are obviously found in water, salt can kill them by disrupting osmosis and drawing water out of them – just as too much sodium dehydrates us, it does the same to plants, but to varying degrees.

Many fresh-water pond plants cannot take as much salt as your Koi. Most plants that you are likely to have in your pond or lake, are glycophytes, meaning that they are not able to tolerant salt.

As salinity level increases, many pond plants become less able to tolerate it. These include amongst others :

water lilies
forget-me-nots
zebra rush
cattails
anacharis
water hyacinths

So, if you are unsure if your plants can take salt or not, always remove pond plants before you add salt to your koi pond.

This is one of the reasons that I usually recommend you avoid growing water plants in Koi ponds. (That and the fact that Koi will eat just about anything ! )

AND – What about blanketweed ?

There are well over 30 species of blanketweed and hair-like string algae.

Some sources say that salt at concentrations between 0.3 % and 0.6% will kill blanket weed in a week.

BUT – yet again it is risky. Both to your fish, and other any pond plants, so take care if you choose to try it.

Can I Measure My Pond Volume Using Salt?

Surprisingly most Koi hobbyists and pond owners do not know their ponds’ actual volume.

Some pond owners may already have accurate information; but a lot of times, especially if the pond is irregularly shaped, it is simply a rough estimate.

I once knew someone who believed he had a 10,000gallon pond, but by using this method we found out that it was, in fact, only just over 3,000 gallons.

That really concerned me.

What if we had used medicine or salt based on the wrong information? It could have destroyed the whole population of his pond.

Here is a way to use salt to get a more accurate measure of water volume.

It is possible to calculate your pond’s exact water volume by using the salt concentration equation. Here are the steps:

Check the salt level of your pond with a digital meter
Add a known weight of salt
Once you are happy that all the salt is fully dissolved, recheck the salt level.
From the difference of the salt level’s new percentage, you can calculate the total water volume as follows:

If you use litres for pond volume, the formula is KG / % = VL, where

KG = number of kg of salt added
% = the change in concentration in % measured using your salt meter ( ie measurement 2 minus measurement 1)
VL = Volume in litres

By way of an example, you estimate that your pond holds about 10,000 litres (very approximately 2,200 gallons).

check the current salt level. eg, water hardness or from a previous use of salt – the reading shows 0.1%
If you were aiming to increase the salinity by another 0.1% in the 10,000 litres pond, you would need to add 10 kg (approximately 22 lb) of salt. So, add a known quantity of it to your pond. (say 5 KG)
After the salt has completely dissolved, re-take the reading – the reading now shows, for example, 0.18%
So – 5 kg of salt has increased the salt levels by 0.08% (0.18% − 0.1%).
5 / 0.08% = 6,250 litres (KG / % = VL )

This means that your pond actually holds 6250 litres – in the UK 1 gallon = approximately 4.54 litres (ie pond is approximately 1400 gallons)

To Summarise

Salt does a fantastic job in helping control bacteria and parasites on a koi’s body.

It also helps balance osmotic pressure when a koi is sick or stressed to help the koi recover.

The use of salt, as opposed to other medicines, means you do not have to worry so much about side effects (with respect to your filter).

Only use cooking salt or PDV (Pure Dried Vacuum) Salt. Other types of salt can contain iodine or anti caking agents which could be harmful to the fish.

DO NOT use any other medication together with salt apart from those recommended by the medicine’s manufacturer as being safe to do so. (Especially AVOID use with Formaldehyde (Formalin))

Working with experience, you can create a salt bath of highly concentrated saltwater solution and put koi in for a short time to quickly kill surface bacteria.

BUT be careful.

Since salt is toxic to koi, do not rush into using salt as a remedy in your koi pond. Think it through and do your homework.

Make your decisions based on your own pond – not someone elses

If your koi are swimming awkwardly or look sick or you buy a new koi – and decide that salt is the best treatment – it is recommended you treat the affected koi individually in a quarantine tank.

This will keep you from using too much salt in the main pond and avoid the risk of the loss of your full koi stock.

At the end of the day, you must remember that koi carp are a freshwater species. Therefore, Koi should not exist in salt water continuously.

If salt is permanently in the water, then it will, in time become ineffective. It would be like if we took pain-killers every day – eventually our bodies would become accustomed to the medication and the effects would decline.