Tweetysvoice, for ducks, I'd abandon all thoughts of equipment made for ponds with fish and turn instead to equipment made for sludge and dirty water. So, I'd go for a submersible sump pump designed to pump out flooded, filthy basements e.g. (this is an Australian site but you get the idea) http://greywatergator.com/d40va-vortex-pump-davey/ I don't know of any pond filter that will actually filter duck water clean enough to return it to the pond. You'd be looking at a big biofilter to get that job done. All in all, the easiest way is to drain the water completely and refill the pond (IMO). I love the way your white duck is beautifully clean even though the water is green Lovely ducks.