Where can you buy the stuff? At a winemaking kind of place, maybe?

I checked wine stores and the product is expensive and granular.
I bought off of Amazon and health food stores.
I just checked Amazon and of coarse with the falling dollar it's $35 a pound.
Make sure it's food grade

Something like this? But seems way cheaper than #35/lb so maybe it's the wrong stuff? http://www.amazon.com/Grade-Pound-Wy...rade+bentonite

Yep good deal. Same stuff

So I did a bunch of hunting around. A biologist that I'm familiar with says that bentonite has enough copper in it to be detrimental to a reef tank. He also said he's analyzed Coral Snow and it is a type of clay, but he can't divulge any more information than that. It is not chalk and it is not bentonite.

Was it food grade that he spoke of

Proteus, do you have snails and crabs in your tank?
If so, then there is not enough copper in the bentonite you use.
Where do you source yours?
Thanks

Yes snail, few hermits, seastar, shrimp. Lots of critters

I buy from health foods store. It's food grade as some people eat it

Food grade can have copper in it since copper is considered to be a good trace element for health.

Yes it can.. I did some reading and found that it can contain copper zinc and silver as they are used for antibacterial.
Though it stated that these are treated and added to the mixture.
Not saying mine does or does not. Though I have a healthy tank