In this blog, I’ll explain why the top Japanese dealers and hobbyists use KoiNendo (formerly known as REFRESH) clay as a mineral supplement to increase the health and shine of their koi fish.

koi clay from japanese mud pondsThis koi clay from Niigata, Japan is so valuable, that some people will even refer to it as “Magic White Clay”!

Let’s start the story at the beginning, when I was a boy in Japan and I would drink water from the tap. Nowadays, like most people, I hardly will drink tap water and choose bottled “mineral” water instead. Why? We drink mineral water not only because it looks healthy, but because we know our body needs the extra minerals.

This is the same reason that Champion Koi breeders add mineral rich clay to their koi care routine that emulates the mud ponds in Niigata, Japan.

You might wonder: Can’t I just throw some average mud in there? I wouldn’t recommend this, as not all clay/mud is created equally. Luckily, you will learn more about the benefits of koi clay for your pond in this article.


Table of Contents About Koi Clay:

What minerals are important to my koi fish?

All living animals require five major nutrients –

  • Protein, carbohydrates, fats, vitamins, and minerals.

While proteins are building blocks for muscle tissue, carbs are the main source of energy, and fats store the energy, vitamins, and minerals support the function of all of the above. Even though vitamins and minerals are rich in koi food, the food by itself, like our human diets by themselves, are not always sufficient to promote normal growth.

Humans obtain minerals by eating plants, animals and drinking water where minerals are dissolved from the earth. Koi generally live in a highly sterile environment, far removed from natural sources of minerals like they would have in the wild. Our human bodies cannot produce minerals naturally, and neither can your Koi fish. So, for this reason, your doctor advises you to take a daily multivitamin to supplement your diet. In Niigata Japan, all the champion breeder’s koi get minerals from the natural clay ponds.

Minerals and vitamins will provide proper function of the metabolism and protect against certain diseases. They are critical to balance and maintain body function for all animals, as they support the function of the heart, metabolism, and building bones/teeth.

Looking for quality koi? Visit our koi farm site online to buy koi for sale.

Why do koi need minerals in water, when they can get it from food?

Minerals can not be produced internally by animals, so your koi must bring minerals in from outside. This leaves only 2 sources of minerals for your koi – food and water.

Choosing high quality koi food for growth and color does provide much of the valuable minerals that koi fish need. But, water should not be overlooked as it is a very critical source of minerals. We drink mineral water, which has minerals already dissolved. Pond water, most of the times, come from city tap water. where the minerals vary on the source of water. The treatment of water is usually deficient as it is highly filtered and sterilized several times before it reaches your faucet.

More importantly, the volume of minerals does not stay in the water forever. Just like food, it is consumed and is a finite resource. Even if there are minerals in your water source, it will eventually be consumed and we cannot predict how and at what rate it is consumed.

Your koi may be in good health in crystal clear water, but that doesn’t necessarily mean the water is healthy – it could still be mineral deficient.

After all, it is very difficult to determine if our koi are getting enough minerals or not, until they start showing signs of poor health.

What koi health problems do minerals prevent?

Lack of minerals in your water could cause the following health problems…

According to a chart of “Demanded quantity of Vitamins and Minerals for carp and its deficiency” (Sato, 1991, NRC 1993), the following are the major issues of Koi due to the lack of minerals:

  • Growth defects
  • Abnormality of Bone structure
  • Low feed efficiency
  • Increases of Visceral fat
  • Poor appetite
  • High mortality rates
  • Abnormal swimming
  • Cataracts
  • Anemia
  • Short bodies

In our own testing, the feeding efficiency of our Kodama Koi Food is about 68.4%, which is quite an amazing number already. By adding extra minerals, the feeding efficiency went up to 82.5%!

**feeding efficiency is a measure of efficiency to convert feed mass into increased body mass**

The bottom line is, if koi are not taking enough minerals, they will have health problems. When they have health problems, they do not look beautiful. When they do not look beautiful, we have problems, don’t we?


Commonly asked questions about Koi Clay

Let’s dive into the details on koi clay questions that will help you learn more on the topic!

How do you deliver minerals to koi? How do I use koi clay? What are the dosages?

Koi in nature live in natural lakes. Koi eat worms with Nendo (clay) at the bottom, which strengthens Koi’s organs and make koi healthy inside and out.

There are three possible ways to assure koi are getting the right minerals.

    • Feed fresh and quality food
    • Change water often
    • Add minerals with clay

silica and vitamin minerals for koi pondsJust one of the three will not solve all the problems. I recommend combinations of the three. Make sure your food comes from a trusted brand and is fresh enough. Please change water at least 10-20% a week. And then finally consider adding a Montmorillonite Clay product to your koi pond.

How to dose koi clay directly into pond – Add 2 oz. of KoiNendo powder to each 250 gallons every 2-3 days. Initially KoiNendo will cloud the water, but it will clear up. It is recommended to dilute KoiNendo with water and add the dissolved solution into your pond. KoiNendo clouds the water at the beginning but will clear up in a few days.

Alternately, mix into feed – Mix 2%-5% to your food. Dissolve KoiNendo into water and mix the solution with food for better absorption. Fed koi after the solutions has evaporated from the food and the food is dry.

Please contact us with any more questions about dosing / using koi clay.

KoiNendo Powder from Akita, Japan or Montmorillonite or Bentonite Clay? Is there a difference?

You can call it montmorillonite clay or bentonite clay, but we call it KoiNendo, these are all different names for a very similar compound, but bentonite is less pure and is an impure ore. 

In my understanding, bentonite clay contains montmorillonite clay. So bentonite clay is not 100% pure clay. Some competing koi clay products uses bentonite clay and claim it is the same and cheap. Finding 100% purity of minerals is rare. It is found in specific locations across the globe and is sometimes named after the location that it was harvested. In the koi world, there are many clay products. Most use Montmorillonite clay as their main ingredients. The clay of course is very rich in minerals. The clay also attracts and absorbs toxic subjects like ammonia to purify water.

DEFINITION FROM WIKIPEDIA – “Montmorillonite is a very soft phyllosilicate mineral that typically forms in microscopic crystals, forming a clay. It is named after Montmorillon in France. Montmorillonite, a member of the Smectite family, is a 2:1 clay, meaning that it has 2 tetrahedral sheets sandwiching a central octahedral sheet. The particles are plate-shaped with an average diameter of approximately 1 micrometre. It is the main constituent of the volcanic ash weathering product, Bentonite. Montmorillonite and Bentonite’s water content is variable and it increases greatly in volume when the absorbs water. Chemically Montmorillonite is hydrated sodium calcium aluminum magnesium silicate hydroxide (Na,Ca)0.33(Al,Mg)2(Si4O10)(OH)2·nH2O. Potassium, iron, and other cations are common substitutes; the exact ratio of cations varies with source. It often occurs intermixed with chlorite, muscovite, illite, cookeite and kaolinite.” Learn more about the difference

japanese koi clay productEven though this is not a human product, this certain type of clay is so valuable that it has been used by humans to cure common maladies with skin, digestion, etc. for thousands of years.

Every summer, breeders in Japan release and raise koi in mud ponds. You will be amazed how big and beautiful these koi will come out of the mud ponds. The body is big. The color is vibrant. The skin is lustrous. The secret we found was in the clay.

The clay in these mud ponds in Niigata were rich in Montmorillonite clay. In Japan it has been a common practice for koi hobbyists who want their koi to grow healthy and beautiful to add clay to their ponds especially and in the USA it is especially important because these koi are often in artificial liners or concrete ponds.

Among all the clay products, it is natural that there are various grades and purity. When you use the clay products, please use the trusted and proven ones from Japan. Our KoiNendo clay mineral comes from the Yasawagi district in Akita prefecture, Japan. This clay is a wonderful gift from Mother Nature, coming directly from the soil and virtually impossible to reproduce artificially. It is used for improving the white skin and strong colors particularly red and black (sumi).

Is it true that clay remove toxins from the water and solve common koi health problems?


Yes! Collectively, these minerals keep the water clean and further help to supply good nutrition.

By dissolving slowly into the water through an ion exchange system and in the same process lowering the levels of less welcome compounds also dissolving into the water, such as decaying organic materials thus minimizing the spread of bacterial diseases. Even though KoiNendo is not a product for human consumption, local villagers who live in the same district where this clay is harvested, use the clay as herbal medicine to heal wounds, fight off diarrhea, toothache and much more!

Benefits of Koi Clay

  • Boost immune system
  • Accelerate growth
  • Improve water quality
  • Enhance color
  • Detoxify and absorb nitrates
  • Improve fish health

These natural remedies are necessary elements to keep koi healthy and improve their color. KoiNendo actually improves water quality and restricts the increase of decaying organic material raising levels of bacterial diseases, thus maintaining your koi in a much more healthy environment.


Best Selling Koi Clay Product In Japan!


Ever since the effect of Montmorillonite clay was confirmed in Japan’s Koi industry, KoiNendo (also known as “refresh”) has been the trusted and only brand of the clay product.

koinendo also known as refresh koi clayThey use the clay mined only in a small district of Akita prefecture, Japan. The white montmorillonite clay, since ancient time, has been used even as a medicine of diarrhea wounds and more. It was even called “Magic Clay.” The clay is definitely something magical to Koi in Japan. The high grade montmorillonite clay has given satisfaction to all koi hobbyists. It is no exaggeration to say that most of the high end hobbyists in Japan use this product.

“REFRESH” is now available in a new package and brand name “KoiNendo” in the US. KoiNendo will provide your koi with quality minerals and a healthy, beautiful look.


Click to Buy KoiNendo from Kodama Koi Supply