Walnut shells are VERY DANGEROUS !!!! They have sharp edges that can cut the inside of your Uro's tummy, it also is harder to clean and can grow bacteria that can infect your Uro.

IMHO .... Pool Filter sand is the best, it holds heat Excellently, there is NO dust or rocks and it is very easy to clean. I have been using it for over a year now for my Uro's and now I'm using it for my Beardies and it has had no adverse side-effects on any of my 5 reptiles.