Montmorillonite / Bentonite Clay in Koi Ponds

The addition of montmorillonite clays to fish ponds have proven benefits. Many koi keepers used these clays with great success. Montmorillonite clays are commercially available under various brand names depending on the country of origin.

Chris On Koi

Fishy stories, facts and myths as told at the edge of the koi pond by Chris Neaves.



The addition of montmorillonite clays to fish ponds have proven benefits. Many koi keepers used these clays with great success. Montmorillonite clays are commercially available under various brand names depending on the country of origin.

Montmorillonite clays, vary in chemical composition and purity, enhance water quality, replenish and augment minerals and remove certain unwanted wastes. The uses and benefits go further than this. Montmorillonite improves the lustre and skin quality of koi as well as heightening the colour. Added to food it is claimed to aid digestion and increase the koi's ability to assimilate the vitamins and minerals required in their diet.

Some claims are made that organic waste such as DOC will be removed from the pond. The ionic exchange capacity is increased. Some koi keepers use very high dosages to remove suspended algae.

There are several forms of brand names of montmorillonite available on the market. Some products are a pure montmorillonite clay. Others are a less pure form and have to be processed to remove and eliminate impurities they are mined with. Some brands claim to have bacteria additives. Other may have additives to the clay such as extra minerals, above what is naturally found in the clay. Whilst others are a montmorillonite clay / zeolite powder formulation.

It is interesting to note that a 100% montmorillonite will form a gel when mixed with water and not dissolve into the system. So in this case a little "impurity" is actually required.

The montmorillonite minerals are composed of hydrous aluminium silicates in the form of extremely small particles. They take up water between their layers, causing swelling, and change the interlayer spacing according to the mineral variety. In addition to being involved in inorganic exchange reactions, they react with and absorb some organic liquids, such as amines, glycols, glycerols, and other polyhydric alcohols.

Montmorillonite was named after its discovery locality, Montmorillon, France in the 1800's. Bentonite (Montmorillonite) was discovered in Wyoming, in Fort Benton shale - hence the name bentonite.

One of the confusing aspects of commercially available montmorillonite clays is the use of two names for exactly the same mineral. Montmorillonite clays are bentonite clays and bentonite clays are montmorillonite clays. They are not two separate minerals as we think. They are one and the same thing. All types of bentonite clays are grouped together under the Montmorillonite or Smectite group of clays. To speak of one is to speak of the other.

Marketing of various brand names using the different terminology for the same thing, in the same text, is often responsible for the confusion that arises.

The description of montmorillonite is :- one of a number of clay minerals within the Smectite Group. It forms by weathering or hydrothermal alteration of other aluminum-rich minerals, and is particularly common in altered volcanic ashes called bentonites.

The description of bentonite is :- a native, colloidal, hydrated, non-metallic mineral of the Smectite Group that is primarily composed of the mineral montmorillonite.

And further - Montmorillonite is a member of the general mineral group - the clays. It is the main constituent in a volcanic ash called bentonite.

Montmorillonite has the chemical formula (NaCa)0.33(Al,Mg)2Si4O10(OH)2.nH20. It has a relative density (specific gravity) of 2.0 to 2.7, and a hardness of 2. Many trace elements and minerals are contained in this clay such as - Silicon Dioxide, Aluminium Sulphate, Iron Oxide, Iron compound, Sulphur Dioxide, Calcium Oxide, Magnesium Oxide, Titanium Dioxide, Potassium, Sodium, Calcium carbonate, Phosphorous allotrope. It is typically white, grey, or buff in colour but may have tints of yellow, pink, or blue. Montmorillonite has a pearly or dull lustre and is translucent.

In some areas the clay is near the surface. In others, many meters of soil has to be removed to get to the clay vein which may be only a meter or two wide and a meter deep, but runs for many kilometres. Just across the border in Mozambique there is a large deposit of bentonite at the surface. It has the most incredible pale yellow colour and is very pure.

In some parts of the world montmorillonite clays were formed during the Jurassic period many millions of years ago. Others originate from later periods. Just like all minerals in the earth, the quality of the deposit will vary from area to area and country to country. Whilst some are of excellent quality others are not very pure.

Montmorillonite/bentonite clays are mined in various parts of the world. A very large deposit and a 90% pure form is mined in the U.S.A. in Wyoming. Other deposits are found in Italy, Cyprus the Philippines, Brazil, England, Japan and the Philippines - and a very high grade is mined in a certain part of South Africa.

Montmorillonite can be found in low grade deposits which will contain about 30% - 40% of its base elements. Whereas a high grade or pure form will contain over 90% montmorillonite in its natural form.

By treating Montmorillonite with soda ash, the meta-bentonite Sodium Bentonite, can absorb water to about 20 times their dry volume and give rise to permanent suspensions of gel like masses. The sub-bentonites, containing calcium become Calcium Bentonite, do not swell to this extent but are still capable of absorbing from their surrounding at a phenomenal rate and contain as many minerals as Sodium bentonite. Calcium bentonites are nonswelling and break down to a finely granular aggregate that is widely used as an absorbent clay. I would recommend that you use a calcium bentoine for the pond for these reasons. The Sodium bentonite also works well but is less easily dissolved into the pon dwater.

Montmorillonite contains a balance of minerals in their natural colloidal form, making it easily assimilated. The minerals present in montmorillonite enhance the production of enzymes in all living organisms.

The deposits containing only 30% - 40% of its base elements (montmorillonite) are considered a low grade in the mining industry. In order to improve the grading (purity) some products have to be refined or processed. The other 60% - 70% of unwanted material has to be removed. Only after refinement does it achieve a 80 or 90% purity as claimed. Montmorillonite are naturally mineral rich clays, formed many millions of years ago under certain geological conditions - therefore, it appears that some products have a small percentage of minerals added to bring the quality up to an acceptable level.

Montmorillonite absorbs water and fluids readily, swelling to a gel-like mass. This property makes it useful economically. Many industries, including textiles and chemicals, use it as an absorbent to refine out impurities. Montmorillonite is also used in drilling lubricants and as a plasticizer in moulding sands used in foundries.

Because montmorillonite clay is used as a human health food as well as in the fish industry, claims by health experts make interesting reading. An average mineral analysis of Montmorillonite by health experts demonstrate it contains no less than 67 minerals, including vital trace minerals. Recently it has been recognized and utilized by the cosmetic industry and by soil experts, who value it as an exceptionally good agricultural enhancement: crops grow faster, taste better, and are more resistant to disease.

Bentonite/Montmorillonite is used to seal dams, in bonding foundry sands, asbestos, and mineral wool, as drilling muds, in portland cements and concrete, ceramics, emulsions, insecticides, soaps, pharmaceuticals, and paints, in the manufacture of paper, for clarifying water, juices, and liquors, and as a water softener to remove calcium from hard water, removing colour from mineral and vegetable oils, also used as catalyst supports and absorbents in petroleum refining. Bentonite is also used as a binder in the animal feed industry.

If you every decide to buld a plastic lined pond use bentonite as a backing. By mixing bentonite into the soil and making it damp you get a wonderfully smooth, flexable protective backing to the liner when you fit it.

The idea that Montmorillonite clays could be used in the remineralisation of ponds originate in Japan. Natural mud ponds are lined with bentonite to seal them. It was also discovered that feeding small quantities to koi and occasionally bathing then in it or adding regulated dosages to the pond resulted in wonderful and significant effects on their colour and lustre. Montmorillonite can be easily added to your daily ration of food in small quantities. This is an excellent idea as it will replicate the koi feeding continuously off minute mineral rich particles on the floor of mud dams. Use calcium bentoinite for koi food.

Montmorillonite is used directly in the pond water each week in a recommended dosage. Use a calcium bentonite in the pond. Some products disperse more easily than others. Some have to be mixed with water before application whilst others can be sprinkled directly onto the pond surface. The pond will clear in about 6 - 10 hours, depending on the amount of organic material in the pond. Do not be worried in a new pond if the water does not clear in a day or two.

New ponds will take a long time to clear as the montmorillonite is trapped into the organic material in an established pond.

The difference between sodium bentonite and calcium bentonite can easily be seen. Sodium bentonite clumps more strongly and has a very alkaline pH. Therefore it is a good idea to rather use Calcium Bentonite in koi ponds.

Although bentonite is found in many clumping cat litters and koi keepers are often tempted to use them in ponds these are best avoided. Manufactures of clumping cat litters often add chemicals to introduce a fragrance to the cat litters. Some cat litters are sprayed with a plastic compound to reduce the dust associated with the clay. Other cat litter have colorants added for commercial appeal. Unless you are absolutely sure - avoid clay cat litters in koi ponds.

P.S. Montmorillonite (calcium bentoinite) also makes a wonderful face pack!