Lee looks like watershield, aka dollar bonnet, brassneria. Best longterm treatment is 2,4-D granular, we sell it as Navigate but also sold as aquakleen. IT is systematic to kill ofroots, glphosate also works but will take mutiple applications to rid of. Grass carp will do little to no control.
With little fish mayb better to drain it and that is cheaper to treat it, then restock after you rid of watersheild, just another thought. Hope that helps will not be around computer again for a few days.