Hey efors those calvus would work and if i were to get some they would be juvies so that they take forever to grow, they take a few years to fully grow out so i would say they wouldnt be an issue, but they are mid to bottom water dwellers and prefer rocky habitats..
the shells will be inside the terrace, if that makes a differenceDon't try to raise the shell piles if that's what you are planning...shellies like to dig.