Sand boa questions.

I just picked up this pair of Sand boa's recently and I was wondering if anyone had any recommendations for a good substrate that they can tunnel through.

http://i57.photobucket.com/albums/g2...psf30611d0.jpg

Have mine on walnut shell sand. I don't feed him on it though, I feed him in a tub so he doesn't get impacted. Put them in what you want. Just don't feed on sandy materials

They're on plain play sand now but it's so heavy. How light is the Walnut shell?