Could you control the spread of duckweed in a tank if you had a bar of some sorts on the surface of the water, penning the plants in, or do their methods of reproduction make this technique useless?
Do you mean you want to put them in one place so that they don't get pushed around throughout the tank from the current, or do you think putting them in a small space is going to stop them from spreading like the great plague? The first option is possible, the second not so much so... :dance2:
Kind of like those floating rings for feeding fish in a certain area? Sounds like it will work as long as the fish/current don't jar any of the bits loose.