How Much Salt In Koi Pond?

Although it is somewhat controversial, the practice of salting koi ponds has a long history, and many people swear by its benefits. But koi are not saltwater fish, and you don’t want to make the water too salty. So, how much salt should you put into your koi pond?

The recommended dose of salt to add to a koi pond is 1.2 to 1.5 pounds of salt for every 100 gallons of water. Salt baths for sick or stressed fish are a generally accepted practice.

Several factors influence good salting practice, with the type of salt being as crucial as the amount. Many people believe you should only use salt baths for sick or stressed koi. Salting is complex, and you don’t want to get it wrong.

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What Are The Benefits Of Adding Salt To My Koi Pond?

Salt, in the proper concentrations, has several benefits.

It enhances the fishes’ ability to produce a mucus coat, which helps protect against bacterial infection. It also adds beneficial electrolytes to the water, and salt concentrations of 2.5 parts per thousand (ppt) or higher control some string algae species.

Salt concentrations between 3 and 5 ppt cause many common protozoan parasitic species such as ichthyophthirius (ich), costia, trichodina, and chilodonella to dehydrate and die, thus controlling their populations. 

However, there are more effective treatments for most common parasites, and medications such as malachite green and formalin do not mix well with salt. For this reason, many people believe that you should not salt a pond at all.

Salt concentrations of 3 ppt protect your fish against nitrite toxicity, which can cause methemoglobinemia (brown blood disease). Nitrite (NO2-) and chloride (Cl-) ions compete with each other to cross the gills and enter the fishes’ bloodstream.

As the chloride concentration in the water increases, the ability of nitrate ions to cross the gills into the blood decreases. Adding salt increases the concentration of chloride ions in the water. Shoot for a concentration of 6 ppm (parts-per-million) chloride ions per 1 ppm nitrite ions.

However, this isn’t a substitute for regularly checking nitrite levels.

The internal salt concentration of koi is nine ppt (parts-per-thousand) or 0.9 percent, considerably higher than the water they swim in because they have concentrated the salt from their food in their tissues.

Osmotic pressure from the surrounding water means that water keeps pushing into the fishes’ bodies through their gills. The fishes’ kidneys must process this absorbed water. 

Adding salt reduces the osmotic gradient between the surrounding water and the fishes’ blood.

 A lower osmotic gradient minimizes the amount of water they absorb through their gills and minimizes the fishes’ kidneys’ work. The energy saved can go toward fighting off disease.

Salt is cheap, has no expiration date, is not bound out of the system by organics or sunlight, and will not affect the functioning of your biological filter system.

However, high salt levels will affect spawning by killing sperm and dehydrating eggs.

Salt can also kill pond plants, with floating plants such as water hyacinth and water lettuce being affected at lower concentrations than bog plants. Rotting plants will remove oxygen from the water, leading to oxygen concentrations in the water being too low for the fish.

Salt will kill fish in too high a concentration, so stay within the guidelines.

How Much Salt Should I Use In My Koi Pond?

Add 2-2 1/2 cups of salt for every 100 gallons of water in your koi pond if you don’t have any aquatic plants. Dissolve it into water in a large plastic tote to create a hypersaline solution, and then mix that into your pond using a pump that you don’t mind rusting. Do not pour the salt directly over your biological filter or skimmer.

You may find information stating the amount in pounds; one cup of salt equals 0.6 pounds. You want to add 1.2 to 1.5 pounds of salt for every 100 gallons (12 to 15 pounds per 1000 gallons).

If your koi pond has plants, add 1 1/4 cups (0.75 pounds) of salt for every 100 gallons of water. Disperse it around the edge of the pond, but don’t put it directly on any plants.

When adding salt, add the salt in stages, and test every ten minutes. Test at the opposite end from where you have added the salt.

Test the salinity of the water after an hour, and partially change the water if the salt concentration is over ten ppt (0.1 percent).

Increase the salt concentration gradually over several days.

Add when changing water (not at other times). Salt does not evaporate, and your filter won’t remove it, so don’t add based on the total volume of the pond but on the volume of water that you replace.

Keep detailed records of the dates you add salt and the quantities.

Do not mix salt with formalin or malachite green.

How Do I Measure Salt Levels In My Koi Pond?

The best way to measure the salinity of your koi pond is to use an electronic salinity meter. Use a good salinity meter such as the KoiMedic. Cheaper meters may measure inaccurately.

Always check salinity levels before adding salt.

 Do not assume how much salt you should add, or you risk increasing the salt to too high a level and killing your koi.

Be sure that you know the correct volume of water in your pond. Assuming that your pond is larger than it is will result in you adding too much salt, which will kill your koi.

An excellent way to determine the volume of water in your pond is by doing a salt concentration test, as follows:

  • Measure the salinity in your pond.
  • Add 0,5 pounds of salt (or an appropriate amount for the volume you estimate your pond to be).
  • Retest the salinity, ensuring that the salt is all dissolved.
  • From the difference in the percentage of salt, determine the volume of the pond using the equation P*12/Δ% = VG, where P equals pounds of salt added, Δ% equals the change in concentration in percentage, and VG equals volume in gallons.
  • Alternatively, you could use the metric formula KG/Δ% = VL, where KG equals kilograms of salt added, Δ% equals the change in concentration in percentage, and VL equals volume in liters.

What Type Of Salt Should I Add To My Koi Pond?

Only use pure sodium chloride. Ensure that the salt is free of anti-caking agents such as yellow prussiate of soda (YPS), which is harmful to fish. 

Don’t use magnesium chloride (Epsom salts), potassium chloride, or calcium chloride. 

Use iodine-free salt, as iodine can raise levels of ammonia and nitrites and cause severe upset to your pond’s chemistry.

When Should I Add Salt To My Koi Pond?

Adding salt in the fall will help fish survive the cold winter, as fishes’ metabolisms will slow down in the colder months. If you have a heater, do not add salt.

Take out floating plants such as water lettuce and water hyacinth first.

Never add salt to a frozen pond to thaw it; the resulting rapid drop in temperature will prove fatal to your fish.

In spring, gradually reduce the salinity by slowly changing the water (over a few weeks).

You can also add salt when you detect nitrites. Ensure that you keep testing pH, ammonia, and nitrites.

Many people believe that you should not use salt long-term, as bacteria and parasites can build up a tolerance, and that you should keep salt for shock treatment.

Are Salt Baths Good For Koi Fish? And How Long Should You Leave The Koi Fish In The Salt Bath?

Many koi keepers who do not favor salt in the koi pond still use salt baths for sick or stressed fish.

You can use a salt bath to enhance mucus production and remove protozoan parasites from the skin, fins, and gills of koi.

 It can also help if the fish has a wound or a bacterial infection.

If fish show signs of stress, such as lethargy, red veins, and clamped fins, you can use it. Preferably do not use it as a substitute for quarantining new fish.

Make up a salt bath 3 ounces of salt per gallon (3 pounds per 100 gallons) of pond water to make a 3 percent solution. Aerate vigorously, and place your sick koi in it for 5 to 10 minutes. Do not leave the fish unattended; this water is the same salinity as seawater. 

When your fish loses equilibrium and rolls over, remove it immediately to clean untreated water for another 30 minutes. Continue to monitor the fish for any signs of stress before returning it to your pond.


Salt in koi ponds is a controversial practice, and everyone has their own opinion on whether to use it or not. However, the general agreement is that salt baths for sick or stressed fish are an effective treatment. Ensure that you do not mix formalin or malachite green with salt.

For use in a pond, the consensus is that one should add 12 to 15 pounds of salt per 1000 gallons of water. Reduce this amount to 0.75 pounds per 100 gallons in ponds with plants, as plants do not handle salt well.

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