I use Repti-Sand, but I only have a handful of quail right now. I pay about $6 for a 5lb. bag, so it may be a bit costly if you have several birds and need a greater quantity. I would just stay away from potting soil with perlite in it (those tiny styrofoam-like white balls) and also avoid another product called Reptilite (not the same as Repti-Sand.) I've seen some people use just regular dirt dug up from their backyards, while others add a bit of ash from their fire pits to this. If you have a spot of sandy soil somewhere on your property, you can just scoop up some of this and put it in large pan for them to bathe in.