Not having a ready source of bentonite I "tested" as follows:
1) I picked up 4 plastic storage containers about 12x12
2) Drilled about 1/2" holes in the bottom of containers
3) Filled each with about 5" of native soil from pond area
4) One "A" container was used for baseline and nothing was added.
One "B" container 1" layer of bentonite was added on top
One "C" container 1" layer of special kitty was added on top
One container "D" had 1" layer special kitty mixed in
in with the native soil
5) all filled to top with water
results: Container "A" leaked the fastest followed by Container "D".
6) added an additional 1" of material to containers B-D
still leaked, but much slower
7) added another 1" of material to containers B-D
Now I was looking for zero leakage, but after 2", water was only leaking a little bit.
So now I have a total of 3" of material either on top of soil or mixed in. Container D seems to leak slightly, but leakage stopped on both other containers..
I also tried this using 2 other kitty litters but they didn't really work to well.
Best of all was the water was clearer in the special kitty container. As an added bonus I had called the manufacturer and they even sent me a coupon for free litter so I could do the test.
