Our 9 pekin quickly grew out of the biggest plastic pool that I could find so I bought one of those big water containers and cut the top off of it so they now have a 250 gallon pool that is about 2 ft deep! They love it! The first week we had it I noticed algae growing and had to drain it and re fill it after about 9 days... well i did think to scrub the algae on the inside so after re filling it, it was BAD after only 4 days. So I just dumped and scrubbed the crap out of it but Im starting to worry about my water bill... i mean... I cant replace the 250 gallons every week! Not very earth friendly either. We have rain barrels but those will be gone in the matter of second with this thing. So my question is... how to I prevent algae? Next year were going to run a koi pond filter to it but we just dont have time this year. I read that there are mosquito fish that will eat algae and mosquitoes but i think the ducks will eat the fish... no?.
OldGuy43 has a recirculating filter system. May not be perfect for what you want, but might help you think of a solution.