Plants will help greatly with keeping a pond clean. If your ducks do not eat the plants LOL
Ducks don't make keeping a pond easy
I tried barley and didn't really see much of a difference, but who knows if I used enough or did it correctly.
I tried plants. They did fine for a few days and then both the ducks and dogs decided they were a great treat and those were gone.
In the end, I have a 7x10 pond that is just under 1000 gallons and a 75 gallon filter box and a decent sized pump (not sure what it was rated anymore) in the pond. Moving water keeps it able to not need to be emptied often. Large kiddie pool of water, had to dump every 3rd day or the ducks wouldn't go near it. This pond, they spend the same amount of time (and there are more ducks now) in the pond, poop just as much in the pond, have addition of tree stuff falling in the pond and as long as the water flows, they are happy to jump in.
The poop settles to the bottom and I just have algae in the water so it is green water.
I drain, hose it out, scrub if needed anywhere and the pond itself is clean - no acorns, no poop, no leaves, nada. Then I hit up the filter box and want to throw up LOL That thing is disgusting. I really really wish I had put a drain in that box as well. It is thick with filtered poop goop! So I drain with a pump, add water, drain, repeat many times, scoop out the goop with a bucket. I should start wearing waders for this project. Pull out the bags of lava rocks and rinse those as best as I can, pull out the AC filter material and hose that out as best as I can and then make sure the box is clean as I can get it. Load it all back in, fill up the pond and box, plug the filter/pump back in and off they go again for another year+
So it may be nasty, but it is a once a year job and that makes it tolerable.
It is nice and clear for a day, 2nd day it starts getting cloudy and then by day 3, you wonder why you cleaned it to begin with.
Last time it was because I had new ducklings and wanted them to swim in clean water they could see in (or I could see them in). So that was last April. I might get around to it at some point this summer or may just wait until fall when it cools down to do it.