Salting a Koi Pond: Benefits & Risks

I used to wonder why the fisheries department in my college added salt to the fish ponds. “What salt were they using?” and “Is it safe?” I asked. I theoretically learned the benefits of salting koi ponds until I established my first fish pond seven years ago. I will explain in this article what salt to use, how much salt to add to your koi pond, and how to apply the salt.

Salt protects koi fish from diseases, fights nitrite toxicity, and improves their gill function. The best salt for a koi pond is pure evaporated sea salt. The high iodine levels in table salt can be toxic to koi fish. They can lead to health issues like pop-eye or shut down koi fish kidney function.

The salt is made by evaporating seawater. It is an ideal salt for acclimatizing and strengthening new, stressed, and sick koi fish. You will learn the benefits of pond salt below. I will also discuss the safe salt levels in your koi pond to balance the electrolytes in the fish tank with the fish’s body fluid. Let’s get started.

What are the benefits of salt in a koi pond?

Here are the benefits of adding evaporated sea salt to your koi pond:

1. Repairs tissues and protects koi fish against diseases

Pond salt covers koi fish with a protective slimy coat to wade off bacterial and fungal diseases: Defense against parasites and bacteria such as columnaris bacteria. Pond salt can also eliminate Chilodinella and Ichthyophthirius within 72 hours. 

The salt also clears trematodes in koi ponds. If a koi fish is bruised from a fight or scratch, pond salt will accelerate tissue repair and hasten recovery. Therefore, koi fish ponds without salt will likely experience more fish deaths than salted koi ponds.

2. Adds essential electrolytes to the pond

Salting koi pond plays an essential role in osmoregulation. In other words, it ensures the salt level inside the fish’s body is balanced with the pond water salt levels. If the pond is too salty, the koi fish will lose water to the pond and may die in a few days. 

Similarly, low salt concentrations in koi ponds result in more water intake and dilution of the fish’s internal fluids. Therefore, adding salt to the koi pond is essential for adding electrolytes such as calcium, potassium, sodium, and magnesium to the pond to ensure optimal osmoregulation.

3. Fight nitrite toxicity

Bacteria break down ammonia in your koi pond to produce nitrites through the nitrogen cycle. The high nitrite concentrations can cause brown blood disease in koi fish. In that case, your fish will suffocate even when the oxygen levels in the pond are right. 

Salting the koi pond will block the nitrite molecules and stop them from entering the fish’s body. However, pond salt will not stop all the nitrites from diffusing into the koi. As discussed below, you must change the water and apply the right amount of salt to your koi pond.

4. Improved gill function

Always test the pH of your koi pond to keep it below 9.5. A pH above that will interfere with oxygen intake in the gills because koi fish gills work best between a pH of 6.5 and 8.5.

Evaporated sea salt will bring your aquarium pH closer to 7.4, improve koi fish gill function, and make them more active. 

5. Pond salt has a long lifespan

The pond salt will not expire as long as you store it properly. You can buy several bags of pond salt from your nearest fish store or purchase in large amounts from online retailers. In the next section, you will learn how much salt to add to the pond.

6. Does not destroy pond filters

Evaporated sea salt is safe for your aquarium equipment. The salt will not damage aquarium filters, thermometers, or heaters. 

7. Inexpensive

As I said earlier, pond salt is made by evaporating seawater. Therefore, it is more cost-effective per unit area than other commercial alternatives.

What is the right amount of salt in a koi pond?

The correct ratio of pond salt to tank size is 1:40. Add one cup of pond salt to every 40 gallons of water. That means you need 2½ cups for 100 gallons, and so forth. Give your koi fish an environment that is between 0.1% and 0.3% saline.

However, that would also depend on the health of your fish and whether or not there are aquatic plants in your pond. For instance, add 1 kilogram of pond salt to every 265 gallons if you are applying the salt to treat an illness. Note that 265 gallons are equivalent to 1000 liters.

An aquatic salt monitor is the best method for determining the salt level in your koi pond. I recommend this affordable Digital Salinity Tester for Salt Water.

What is the right type of salt for a koi pond?

Not all salts will promote the recovery of your koi fish. The right type of salt for a koi pond is a non-iodized Sodium Chloride salt. Depending on your pond temperatures, it takes 2 to 3 weeks for the salt to remove parasites.

Unlike table salt, non-iodized salt has no additives. An excellent example of the right salt for a koi pond is evaporated sea salt. It adds potassium and calcium electrolytes to the water for optimal osmoregulation, improves gill function, and fights nitrite toxicity. 

Is koi pond salt safe for plants?

Koi fish can tolerate higher salt concentrations than aquatic plants. Where there are plants, keep the salt concentrations at 0.1%. If your koi fish are sick, raise the salt concentration to 0.3%.

However, that high salt might damage aquarium plants in the pond. To avoid plant damage, isolate the sick koi fish and add salt to the quarantine tank. 

How to add salt to a koi pond (koi salt treatment)

Follow these steps to add salt to your koi pond:

  1. Calculate how much water is in your koi pond. For every 100 gallons, use 2 ½ cups of salt.
  2. Sprinkle the salt evenly around the edge of the koi pond.
  3. Change the water and salt every two weeks for sick koi fish.

With the optimal salt levels in your pond, you’ll have healthy fish and a generally healthy pond.


G. Melanie. (1998). Nitrite Toxicosis in Freshwater Fish: “Brown Blood Disease.” Purdue University.

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