Bill D, here is where grass carp may be your answer, besides the Eurasian Millfoil problem you have. For years I have had a tiny area about a yard square of duck weed in my pond but it has never gotten out of hand. I have always guessed that it was because of my grass carp. The problem with grass carp is getting the right amount for the job in the pond. I usually put 6 in at a time and watch for results.
If you will do a Google search you will see that grass carp will eat duck weed but it is not there favorite thing to eat.
