I'm still happy with the sand system. I'm not sure it really has any advantages over other media, since it does require a fairly regular - every 2 days - brush off of the algal buildup. It's also unfortunate that the spot I chose to do this experiment has gotten pretty shady. It will be hard to judge/compare growth, as my aquapondics grow beds get much more sunshine.
The sand is definitely compacting. I'm planning on adding another bag of sand to top off each of the grow beds. I'm considering getting pea gravel instead of sand to try and minimize some of the algal mat effect - hoping that the increased distance between the gravel will still allow water to percolate through it. The sand gets so covered in algae that the water starts to pond.
All in all, though, things are going quite well!
BTW - these photos are over a week old. I tried for at least a week - maybe longer - to log in to submit this post on Blogger, but it wouldn't let me log in. Something was very wrong system-wide apparently, and it took Google a surprisingly long time to figure it out and fix it (in my opinion).