Clay substrate

[pumpkin]

I am in the process of setting up some concrete rings to be used as outdoor tanks to grow aquatic plants in. As a substrate I was thinking of using clay in the form of "Kitty Litter". Has anyone used this form of substrate before ?. Dave Wilson from "Aquagreen" in Australia has mentioned that some Australians are using it in aquariums but I am wondering if anyone in SEA ( Sth East Asia ) are'/have used it.
Your thoughts would be appreciated.
Thanks
Bob

[barmby]

Do you have the content of "Kitty Litter" ? Is it pure dirt ?

[pumpkin]

Thanks for the response Barmby
From the packet of "Cat san" that I saw at a Dept store yesterday the contents said 100% Calcium bentonite. I will check the shops at JJ & sunday market ( in BKK ) on Wednesday to see what "Kitty Litter" states. I believe Calcium bentonite is actually a form of clay. This sort of material is now used by Reptile keepers as well. I have asked friends in Aust. & will await their reply.
Bob