The 1000 gph filter won't be nearly enough. You need to be able to turn that water more than once an hour.
I know our pump isn't pumping at it's max capacity and is likely part of our green poopy problem, but the ducks are still fine to go in the pond where after 3 days, their big kiddie pool was disgusting and they'd go nowhere near it. And it has been over a month again since I've drained and cleaned it.
Find the biggest container you can get and turn it into a filter. Read up on skippy filters and see if you can find some cheap ideas.
If you have a water bill, it will be worth it to invest in a reasonable filter system, otherwise you will be draining and filling that pond more often than your water bill wants you to.