Aquathol K at 1.9 gals/acre foot plus Hydrothol 191 at 0.5 gals/acre foot has been effective at controlling the floating heart species. However, as Kelly mentioned this is a very hearty weed and you will likely have to do retreatments. I have seen through active management (several retreats) of this species that densities can be reduced to very small patches. Then you might be able to physically remove plants that remain.
