David, I took a look at the duckweed you provided....WAAaaaayyyy too much reading for me, however here are some photos. This one is of the water coming into my grow bed from the bio-filter. As you can see, I have other water plants in the grow bed also.



Here are two photos of the Styrofoam ring that keeps the duckweed from escaping the grow bed. It doesn't have the water flow of a waterfall, but it is actually moving at a pretty good rate.





Here are a couple of photos showing the water flowing back into the fish pond from the grow bed. That white blur you see below the surface is one of my 24 " breeder Koi.





And in answer to your question about the sump tank, yes it does contain baffles that I installed. They are plastic afixed in place with silicone