between the ducks and my 1 red eared slider that's still around, and direct sunlight, my kiddie pond is a mess all the time.. i need to get something with filtration....
before i had birds, when i had just my turtles, this was one of my favorite websites for pond stuff...
Drs Foster & Smith....
http://www.fosterandsmithaquatics.com/pond-supplies/pr/c/5163
they have stuff for lots of animals.. not chickens and ducks and etc, but a lot of that stuff can be adapted.. and they have lots of info on their website and in their regular in your hands flip the pages catalogs....
i keep thinking the sand at our new house is ssoo much easier to dig than the last place we lived and i should just build them a real pond done right, but then i remeber i have to get power to it somehow to plug in a filter... lol.. doh....
a couple things that might be relevant from when i had just turtles in the pond....
circulation helps a LOT with algae control and keeping the water clean... even if it's not a filter, and justa powerhead to move the water around...
and there's a carbon/charcoal for the filter that has ammonia in it to.. it's called ammocarb i think.... that was awsome to keep the water clear and the smell gone.. way better than plain carbon filter stuff...