I don't think its possible to have too many shells for a shellie tank.  For just a pair though at least 5 shells IMO.  Let them choose which one they want to live in because the seem to never live in the ones you want them to.  And like Pittbull said, sand is the way to go!
  And like Pittbull said, sand is the way to go!
				
			 And like Pittbull said, sand is the way to go!
  And like Pittbull said, sand is the way to go! 
	 
	




