The BentoMat would be better for assuring a uniform layer of clay and not
allowing the fish to root around in it. The Bentonite powder is what is
used in the koi grow out mud ponds, and they keep it stirred up rooting for
worms, insects, and other goodies. If the sodium bentonite is mixed with
the soil as an amendment, it may stay dry enough to make the expansive
properties beneficial. The part that is stirred up in the water wouldn't
matter if it was sodium or calcium.
--
RichToyBox
http://www.geocities.com/richtoybox/pondintro.html


"Nicholas Walker" wrote in message
...
Thanks to those kind helpers.

Research has revealed the existence of Sodium Bentonite powder and
"BentoMat" membrane, which is Bentonite sandwiched between a geosynthetic
layer.

Does anyone have any experience of these products?

Haven't found a UK price yet but the stuff reads like a real cure-all

Blocks all leaks, natural product, self-sealing, natural-looking

Many thanks again

Nick Walker