Yes it's safe just the shells, sterilize them, boil in a pot for 15 minutes make sure you use aqua-sol for prevention of deseases I've been using it for years.
While i'm waiting for replys i've went ahead and started soaking the sand and rensing it. So i think i've about got everything out of it that shouldnt be there. Im just a little paranoid to put it in beause i've never tried it before.