Okay so right now my beardie is on a mat but I absolutely hate the mat. I had it at first because I know young small dragons shouldn't have sand because of digestive issues along with other things. My beardie is 11 inches now and j want to get sand. Is he big enough for sand? And I heard calcium sand found at like petco and stuff is bad for your dragon. I found some sand by Zilla called the desert blend and it says is ground walnut shells, is that okay? If not what do you recommend?