I'll take a shot at this for you...With or without sand...
Just add a dozen small pieces of very low profile (1-4") rocks on the bare bottom. Float a ball of Chaeto that covers up to 1/4 of the tank surface, pump water (return?) onto the edge of the chaeto ball so it tumbles just a little to produce visible motion. Harvest it as you see fit to export nutrient. You can tie the chaeto ball in place with a string from above so it doesn't travel around the tank.
If you can, move the clam to the one-thirds point in the front viewing frame of the tank. Move it forward to be a focal point in your 'scape, just a few inches behind the front glass. Do the same thing on the other side with the tall rock on the right. Move it a bit to the left to the right side's third's point. Also move the tall rock forward to about the center, front-to-back, of the tank floor. Stack some rock next to and leaning against the left side of the tall rock to form a swim through or even a cave using the slight undercut of the tall rock as its right wall. Move the smaller clam just a bit off-center, closer to and partially in front of the large rock so the two are suggestive of an alcove and the swim-though/cave is to the clams right. Make the swim-through opening as large as you can. If it is to suggest a cave, you can visually block the back side of what would otherwise be a swim-through with small rocks and plants.
Group the small rock in low lying clusters kinda like a few mini-bommies separated by a few to several inches of bottom leaving channels for the Mandarins to roam and browse. Leave a large beach-like area in the front of the tank extending to and behind the small clam and wrapping around the tall rock. Put taller plants behind and outboard of the tall rock, somewhat in the corner. Situate the chaeto ball to the rear of the tank a bit off-center. Plant low plants at the front left of the tank in the corner and in the real left corner, taller ones to the rear, maybe on a mini-bommie. The front right corner should clearly be dominated by the tall rock and its swim through and its clam. The left side highlights the big clam at a prominent 1/3 point with bottom space (sand?) around it and flanked on its left by low, colorful plants.
'Scaping Recommendation: get some molding clay (real cheap at a craft store) and mock up your layout, roughly. Work on wax paper that is taped to stiff cardboard. You can do a model in 10 minutes or less. Do several of them. Cut a frame out of cardboard to represent the tank viewing frame. Look at the model through that cutout. It is a great way to move things around, get it right aesthetically and not have to mess around in the tank before you have a solid idea of what you will like.
Whattaya think???
fab
