An artificial additive-free top soil product can be used but most contain pieces of twig and other organic debris so for a pyxie you should take this into consideration. Of the products sold at home depot (and walmart for that matter), I know of researchers who maintain frogs and toads routinely on Miracle Grow organic choice potting soil. Personally I use a debris-free potting soil when I can find one. If you have a garden that does not have pesticides (herbicides or insecticides) then why not just use the soil from there?