Hi Jim, I think the drawback to your system is that it is too small. I much prefer the larger longer look to the small hexagon. I think that one problem is that viewing is made kind of difficult. I am imagining lighting illuminating the entire surface and getting glare everywhere. I think you can get a custom system that is made a bit different from the hex tank that would incorporate both the hex part and a longer extension off the end that would more effectively display your clams. I also think that maybe a rectangular system might be nice, maybe one of those compartment look down display systems so that each clam could have it's own home and you could easily look down on them, or remove the compartments and have a single large tray. I think that with the exception of problems with spawning (since clams have squirted out of the water according to some stories), you could have an excellent system if you left the depth at only 6-8". Or, have a 6" DSB in a 12" deep system.
Also, I was under the impression that black sand was either silica sand which could be detrimental according to some sources, made of broken glass which could be too sharp and abrasive, or that it was from crushed lava rock which would leach a lot of undesireable elements into the water.
Not trying to knock your system, I think a shallow tank for clams is a wonderful idea that I've also toyed with in the past, just some suggestions, take them or leave them (your systems all look great regardless and I always enjoy your clam pics).
