It's hard here in thailand to find water plants when you do they can be…
Problems with water iris in pond
I would ask you to think twice before putting water iris into pond. And yes they help with water quality taking nitrate etc out of the water and they don’t get beat up so much by the fish as water lettuce.
But and its a big but the fine old root fibres break off and are not eaten by the fish. They make there way to the pumps blocking them or just laying on the bottom of the pond and adding to the water colour all of which is going to take a little time to clear.
So now we have changed over to lilies they are growing in fast giving more shade without mucking up the water .