Awsome perception of depth with your shadowbox, no arguments there.
Scifi_3d_zoo did raise an interesting point though. Could you get a similar effect by using a printed decal?
I believe that it's to easy to dismiss that with the statement that it won't alow getting the desired 3d effect. Afterall, the shadowbox also only creates the illusion of depth. A good photograph tweaked using photoshop might be able to approach a similar effect. Clear advantages are that it will be cheaper, more easy to 'build', not requiring additional lighting and the tank can be positioned against the backwall. Possible enough advantages to overcome any potential loss in 3d effect?
I don't know if it would work, but some day I might try since I really, really like the effect you've achieved here.