DIY Duck Pond Filter

A while ago I posted about our garden pond and homemade filter swamp. Prior to building the fish pond, we did a smaller pond for our pet ducks & goose. This one is basically just a buried stock tank next to the bird coop.

Since water birds produce a lot of umm… “dirt” in the water, we wanted a pretty beefy filter to keep the water clean. The pond includes a submerged pump (Tetrapond 1000) with plumbing that runs up to an external barrel. The barrel drops water into the bottom, then filters it upwards through progressively smaller layers of stones, pumice, gravel, and composite filter media. The filtered water runs off the top of the barrel and back into the pond.

That thing in the center of the barrel is an aerator tower. Water is pumped into the side of the large plastic pipe, which has an opening at the top for air. The water then drops down inside the large pipe, ideally pulling some air along with it and mixing the air in with some nice splashing.

Here’s what the aeration tower looks like before it went into the barrel. The “legs” at the bottom hold up the first layer of filter media (larger rocks / gravel on plastic grating) and maintain an open space at the bottom where solids can settle out. Water comes in near the top of the tower through a small pipe with a 90-degree fitting inside. This makes sure it drops straight down the center of the tower to maximize splashing.

Below shows the tower inserted into the barrel. At the bottom you can see angled pipes with 90s that inject the new water in a circular pattern into the bottom of the tank. This helps stir the bottom chamber to avoid clogs and let the sediment settle out.

Here are a couple rough sketches I made while planning this out. Neither of these shows exactly what we did with the filter media. Some websites suggested things like floor scrubber pads, but we ended up using layers of large rocks, gravel, and pumice, then topped it off with some filter mat rolls intended for koi ponds. The idea is not only to filter out solids, but to create a lot of different-size crevices and surfaces for beneficial bacteria to grow. The bacteria does the bulk of the cleaning by removing dissolved nutrients from the water.

The final setup is seen below. We have water-loving plants growing in the top of the filter barrel. The red thing in the pond is a float valve that tops off the pond from a rain barrel on the bird coop. The other white pipe coming in from behind the coop is an overflow from the rain barrel, so when it’s full the extra rain water also goes to the pond.

So far the filter has worked great through several years of use. Without filtering, the duck pond would grow mats of stringy slimy algae. With the filter, any green stuff grows inside the filter media and the pond water stays crystal clear! In fact, one year we accidentally raised goldfish in the bird pond!

In the winter we shut all this down and drain the whole system so it doesn’t freeze. The barrel filter has a large cleanout valve at the bottom, it’s large enough to stick a hose in and wash out all the sand that builds up. For the winter the birds get a smaller shallow pond (kid’s sandbox) that’s small enough for a submerged heater to keep liquid.

Here’s the video tour of the finished pond system: