Bentonite clay is available in 50 pound bags from every well drilling supply company in the country. Most water well drillers have it as well, although it won't be as economical as from the drilling supply places. It is commonly used to seal leaks in ponds, to seal abandoned wells, and for well drilling. I just bought 10 bags of it to work on my earthen pond for $11 a bag.

What does koi clay do? Sorry about the stupid question:-)

Well drillers use Sodium Bentonite clay as a lubricant, not Calcium Bentonite clay.
Sodium Bentonite clay can swell 115 times when mixed with water.
Calcium Bentonite only swells to twice its size when mixed with water.
That is why it is used in ponds as a colour enhancer for koi, plus it's flocculation characteristics (see link below Calcium Bentonite section for explanation) can help make the pond water clear and shiny.
The clay known as "Koi Clay" is Montmorillonite clay named from the region in France where it is mined and it's common name is Calcium Bentonite.

Water treatment plants use Calcium Bentonite in water purification. It is also used medicinally for humans and animals alike, also in skin beauty treatments, Etc.
It is known as "the clay with a thousand uses".
In the UK it is known as Fullers Earth but Fullers Earth can be made up of many different clays.

Some unscrupulous people will sell Sodium Bentonite as Montmorillonite "Koi Clay", which it is not.
"Horton"

Here is a link that might be useful: Bentonite information.

Calcium bentonite tends not to be the best clay to use for sealing ponds for the simple reason that it doesn't expands sufficiently to give a good seal. I suspect that you'd find they are most likely using sodium bentonite, or in some cases, kaolinite. In the use of clay for sealing basement walls, for example, it is sodium bentonite which is typically pumped/applied in and around the footing and walls of the structure, again because of it's expansion properties. That being said...what is, I think, important is that folks can find an inexpensive source of calcium bentonite without paying the outrageous prices for something which is most likely packaged from the same source and then marked up ... a lot! Thanks Horton, for locating an inexpensive source for you folks up Nauth! At least they won't have to worry about Customs!! One other point...I'd suggest that you make sure you get a finer particle size if available. The reason I recommended something similar to the Panther Creek PC-200 in another post is that greater than 70% passes through a 200 mesh screen. Some of the bentonite sources are a bit coarser and may not provide the same surface area or the same ion-exchange properties. Just a thought/recommendation.
---David

Do you still have that source for calcium bentonite that is more affordable? I'd sure appreciate the phone number and web address. Thanks

Betty, e-mail me and I will send you the details.
"Horton"

Here is a link that might be useful: E-mail link

I have lately been notified that unfortunately the source I had for the inexpensive Calcium Bentonite ("Koi Clay") has ceased shipping it out in "small amounts" (i.e. 50lbs bags/pails) to individual customers and now only ship it out by the pallet load.
They state their reason for the change is because they no longer have the staff now, due to cutbacks, to take care of the small individual orders.

I hope all the many folks who have contacted me through the years for the information re, the source of the inexpensive Calcium Bentonite, did however managed to purchase it prior to the company stopping shipping it out in "small" amounts.
"Horton"

Hi there, I'd still like to know the source as I will buy a pallet....I have a large area to improve....can you please supply the source? Thank you ever so much, Kim