I'd go with a Tanganyika with Callochromis, Enantiopus, or Xenotilapia species for sand... Cyprichromis Leptosoma "Utinta" for the open water... and Eretmodus for the Rocks... I used to like Shell dwellers before I got my cyprichromis... since I got them... My brevis never uses the shells... he is always at the top of the tank swimming with the Cyprichromis