I would try store bought dirt.I tried sand like that, but they seemed more interested in eating the sand than in eating their feed, so I removed it. Plain dirt from the back yard is very high in dry, powdery clay that turns into a slick, snotty, 'stain everything red' mess when wet and sand derived from volcanic rock; do you think I ought to give that a try instead of the store-bought sand? @Texas Kiki