Calcium Montmorillonite (bentonite) Clay is a “living” smectite clay that has been used in hobby and farm ponds for many years. It’s packed with upwards of 60 bio-available minerals and trace elements, plus anti-bacterial, anti-fungal, and anti-parasite properties.

Montmorillonite Clay is one of the secrets of champion Koi, Arowana, Discus, Guppy, and other fish breeders, who report:

  • Improved color
  • Healthier skin, scales and skeletal system
  • Improved immunity, including disease & parasite resistance
  • Increased egg production
  • Less deformities
  • Increased fry survival rate
  • Enhanced growth rates
  • Larger fish
  • Stronger and larger fins with improved resistance to splitting
  • Increased lifespan

Scientific studies for aquaculture have supported these claims, reporting:

  • Improved digestion and nutrient absorption
  • Support of intestinal microflora
  • Anti-bacterial activity in vivo
  • Larger fish when Montmorillonite Clay is supplemented, even when fed less food
  • A study by the Yobe State Aquaculture college concluded that Montmorillonite clay can completely replace a mineral/vitamin premix in catfish fingerling diets with no adverse effect on growth. The substitution also improved skin quality of the test subjects after only three weeks of feeding.
  • Organs are protected from heavy metal damage
  • Protection from Mycotoxin and other toxins
Montmorillonite Clay Natural Fish Food
Mollies, B. striata, P. siamensis, and a Swordtail dine on Buggy Bottom Bites fish food containing Calcium Montmorillonite Clay in our aquarium.

This all comes as no surprise when you consider that clays constitute a large part of sediment in oceans and other bodies of water. It’s a critical part of the natural habitat and ecosystem of fish that has been lacking in captivity.

Calcium Montmorillonite Clay in the Aquatic Environment

While past popularity has been largely limited to pond owners, Calcium Montmorillonite Clay is currently being explored for aquarium use. It is most commonly used as a therapeutic bath for injuries, parasites or disease, after reports of success reached North America from overseas breeders. It’s also used as a mineral supplement for aquatic plants and fish (fish absorb minerals from the water supply as well as through ingestion).

In the aquatic environment, Montmorillonite Clay binds toxins and heavy metals to a degree that far outperforms charcoal and other filter products, plus it supports beneficial bacteria. Scientifically speaking, most bentonite clay minerals have peculiar adsorption arising from their layered structure, charged layers and active edges. The layered structure provides inter-layer space to host guest molecules and ions. Charged layers and “broken edge” sites attract varieties with opposite charges through Van der Waals force. Such features allow clay minerals to be used as adsorbents for the removal of heavy metal ions from water. Calcium Montmorillonite Clay can also be effective adsorbents and absorbents of oily pollutants and animal waste.

As an added benefit, Calcium Montmorillonite Clay also helps to stabilize pH and control algae. Suspended green algae can be cleared by treating the water with Montmorillonite Clay, which binds with the algae and allows it to settle or be removed by filtration. While sodium bentonite may be used in ponds, it doesn’t dissolve as well as Montmorillonite Clay and will inevitably result in equipment damage.

Our experience with the use of Montmorillonite Clay in aquariums has been very promising at the therapeutic level. We have also seen positive results with the addition of Calcium Montmorillonite Clay to our Shrimp and Apple Snail tanks. We add a dash or two from a small-holed salt shaker (comparable to a pinch of salt) per approximately 20 gallons during each water change. While too much clay can cloud the water, you may want to try it in somewhat larger quantities in a quarantine tank for the temporary treatment of disease. It can be added to a box filter, or be mixed into water and then added to the fish tank. Too much clay, however, may cause larger changes in pH, interfere with gill function, clog drains or damage mechanical filtration.

Calcium Montmorillonite Clay in the Fish Diet

Aquatic animals have been ingesting clay since their early existence, purposefully or inadvertently. There’s even a species of shrimp that lives its entire life in clay.

If you make your own fish food, Montmorillonite Clay can be added as a highly bio-available, colloidal mineral supplement, with added preventative, healing and anti-parasite benefits. It also balances the body’s pH and assists in toxin removal (including aflatoxin), while optimizing the digestive system. Our fish have been ingesting it for several years in dehydrated Bottom Bites fish food. As a bonus, it turns fish waste into a mineral-rich plant manure that benefits both aquatic plants and terrestrial plants if you use aquarium water in your garden.

To avoid impurities and low effectiveness that may have a negative impact on delicate aquatic pets, we recommend you only use human edible grade Calcium Montmorillonite Clay, as opposed to cosmetic clay, pond (animal grade) clay, or generic healing clays (which can be virtually any type or grade of clay). Lower grades sometimes have a lower sticker price, but their effectiveness can be as low as 25% of high-grade Calcium Montmorillonite Clay.

Since much of this information is new to fish-keepers, we’ve included an list of sources below to help with your research.

??? Have you used Calcium Montmorillonite Clay in your pond or aquarium? Please share your experience in the comments below.

Hu, C. H. Effects of Cu2+-exchanged montmorillonite on intestinal microflora, digestibility and digestive enzyme activities of Nile tilapia. 2007.
Ismaila M. Montmorillonite Clay As Mineral Supplement In The Diet Of Catfish (Clarias gariepinus). 2011.
An evaluation of mineral supplementation of fish meal-based diets for African catfish
Eya, Jonathan C. Effects of Dietary Zeolites (Bentonite and Mordenite) on the Performance Juvenile Rainbow trout Onchorhynchus myskis. 2008.
Antibacterial effect of Cu2+-exchanged montmorillonite on Aeromonas hydrophila and discussion on its mechanism. 2010.
Haydel, Shelley. Broad-spectrum in vitro antibacterial activities of clay minerals against antibiotic-susceptible and antibiotic resistant bacterial pathogens. 2007.
Ellis, R.W. Reduction of the Bioavailability of Aflatoxin in Trout Feed Containing Clay. 1999.
Jaynes, William F. Influence of Soluble Feed Proteins and Clay Additive Charge Density on Aflatoxin Binding in Ingested Feeds. 2011.
Mosaad A. Abdel-Wahhab. Adsorption of sterigmatocystin by montmorillonite and inhibition of its genotoxicity in the Nile tilapia fish (Oreachromis nilaticus). 2005.
Song Gwan Kim. Effects of Montmorillonite on Alleviating Dietary Cd-Induced Oxidative Damage in Carp (Carassius auratus). 2011.
Wei Dai. Effects of Montmorillonite on Pb Accumulation, Oxidative Stress, and DNA Damage in Tilapia (Oreochromis niloticus) Exposed to Dietary Pb. 2009.
Anderson, Donald M. Controlling harmful algal blooms through clay flocculation. 2004.
Matson, Sean E. Specific pathogen free culture of the Pacific oyster (Crassostrea gigas) in a breeding research program: Effect of water treatment on growth and survival. 2006.
Avnimelech, Yoram. Sedimentation and Resuspension in Earthen Fish Ponds. 1999.
Zhou, Chun Hui. Keeling, John. Fundamental and applied research on clay minerals: From climate and environment to nanotechnology. 2013.
Schils, Sheila, Ph.D. What Was Old Is Now New. The Use Of Clay In The Fight Against The Harmful Effects of Ammonia.
Lan, M. Rare Earths: Forbidden Cures. 1995.
Dextreit, Raymond. Our Earth, Our Cure. 1993.
Abehsera, Michel. The Healing Clay. 1979.
Knishinsky, Ran. The Clay Cure : Natural Healing from the Earth.  1998.
Engel, Cindy. Wild Health: Lessons in Natural Wellness from the Animal Kingdom. 2003.

✔ You may also be interested in reading:
Increase or Decrease Freshwater Aquarium pH Naturally
Natural Prevention and Treatment of Aquarium Fish Parasites
Natural Pet Protection from Aflatoxin (and other Toxins) with Montmorillonite Clay


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15 thoughts on “Benefits of Montmorillonite Clay for Pond and Aquarium Fish

  1. Clay really works for shrimp! They’re healthier and a have a lot more offspring, but I don’t know if it’s more breeding or more survive. Color is amazing too.

  2. I was skeptical when I clicked the link I admit but it looks like you have all your ducks (fish?) in a row. It’s an interesting concept indeed and as you explain it makes sense. I don’t know if I’ll try it or not but I might.

  3. Impressive list of references. It’s nice to read an article by someone so well studied. Keep up the good work.

  4. How have I gone so long in fishkeeping without knowing about this??? I can’t wait to try it!!!

  5. I’m too lazy to make my own fish food so I buy the Bottom Bites with clay. I agree it makes a big difference to feed natural food like that.

    • That depends on the batch size, but a little goes a long way. Half a tsp of high-grade Calcium Montmorillonite Clay for every five cups of food would be plenty for most fish.

      Thanks for the great comments everyone!

  6. I don’t have a koi pond since we moved to a condo. I miss it! We used clay but I can’t recall what brand.

  7. A breeder told me about clay many years ago when I bred goldfish. I started using it in my aquariums too and you’re not kidding…..the stuff is fantastic.

  8. We’ve used clay in our pond for algae control and the fish are healthy. We’ve never lost one over the winter either. I’m glad it’s helping them in other ways too. I’m going to get some more this year and try it when I make fish food (which I’ll be doing for the first time thanks to you).

  9. I don’t know if it’s the clay or not but my fish have been improved greatly since they started eating Bottombites. They’re super active and breeding like rabbits!

  10. I wish you’d write about fish more often because your research is outstanding. Thanks for the clay info, I’m going to check it out.

  11. I saw your post on Twitter and it made me curious since I love my fish. Very interesting post.

  12. WOW!! I’ve heard of clay in ponds but I didn’t know it had so many uses and benefits!!

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