Excellent points, thanks Diana.
1. Yes, I will be allowing for the excess return (and testing extensively in the garage).
2. Great idea for testing, I will definitely try that out.
3. It will be viewed from the 'long' sides (front and back). Yes, I realize one side will have plumbing - that's my office viewing angle
4. I agree with the floating plants, but perhaps the duckweed could be tied to a suction cup, 'anchoring' it? (not even sure I'd use duckweed, but would be nice to have that option down the line)
5. Could the debris along the substrate be moved/pulled upwards with a high enough turnover rate? I'm hoping the shrimpies will help with sunken debris.