I like Parrots Feather, Mare's tail, water lilies, duckweed, Azolla, Sedge plants in pots.
Parrots Feather:
Mare's Tail to the left in a pot:
Hardy Water Lilies:
Duckweed, the fish will eat it so keep some outside the pond in a container of some sort:
Azolla is a pretty neat little tiny floating plant also:
There are many different kinds of Sedges and Carex plants that suck up lots of mucky nutrients very well from you pond. They are grassy type plants like the big one I put in a pot in the pond and some are planted in between the rocks w/their roots in water. That is some duckweed floating near the fake ducks that I throw in once in awhile for the fish to eat:
So many more plants that others can let you know about also. Hope this helps some.