Pond Filter




My backyard pond consists of a 2000 gallon main pond and a 300 gallon header pond. Water is recycled from the main pond to the header pond which provides settling/filtration and biological treatment. Originally, this was achieved by passing the water through about 15 cubic feet of lava rock. Although this worked well for more than 15 years, annual maintenance of the lava rock was very labor intensive. Each year, I removed the lava rock by shoveling into buckets, washing it on an inclined screen and reinstalling it. This normally takes 2 days; as I got older, it got harder.

In looking for a better way, I replaced the lava rock with Bacti-Twist plastic media which provides surface area for biological treatment; however fine particulate matter passed through this media and the pond water was not as clear as previously. In looking at commercially available pond filters, I could not find anything I liked. Most were either for much smaller ponds or were external to the pond, which I did not want. I next experimented on a small scale with polyester fiberfill and found it did an excellent job of filtration. I then built my own pond filters using polyester fiberfill for the filtration media.


  • Note: the size of the following materials should be modified based on the size of the filter desired
  • I built two filter boxes and connected them in series

Container: Sterilite 116 Qt Ultra Storage Box, Home Depot, $18 ea

PVC pipe: 2”, 10’ piece

Pipe fittings: as required I used unions to connect the filter boxes and to connect to the feed pipe. I put a pipe cap on the end.

Support grate: 4’x8’ vinyl diamond privacy lattice, Home Depot, $30 This is much more than necessary; a smaller sheet would suffice.

Filter media pads: Matala low density black, thepondguy.com, $35 ea I selected this option because it has the most open space. The purpose of the pad is to retain the polyester fiberfill.

Polyester Fiberfill: Walmart, $7; A 12 oz. bag will do two filters my size. This is replaced each season.

Sealer/glue: Goop, Home Depot

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Step 1: Construction Details

The pump discharge flows into the 2" PVC pipe with 1/2" holes. The flow is upward through the support grate, through the polyester fiberfill, through the filter media pad, exiting the container lid.

Step 2: Prepping the Container

Holes are cut near the bottom of the container ends to accommodate the 2" PVC pipe. The pipe is glued to the container inside and out with Goop. Openings are cut in the container lid to allow flow from the filter.

Step 3: The Support Grate

The support grate is cut from PVC lattice to fit snugly in the bottom of the container about 3" above the bottom. The support legs are cut from 2" PVC. The lattice is scored with a hole saw to accommodate the legs, which are glued on with Goop. I placed 4 bricks in the corners before adding the polyester fiberfill to prevent flotation of the filled container.

Step 4: Polyester Fiberfill

Polyester fiberfill is added to within about 2" of the top. On my last modification, I used rolls, rather than loose polyester, which I found less likely to result in channeling and easier to remove.

Step 5: Filter Media Pad

The purpose of the filter media pad is to retain the polyester fiberfill. It should be cut to fit snugly at the top of the container. I used the low density version because it was the stiffest. A box cutter worked fairly well to cut the pad to fit.

Step 6: The Lid

The lid is held by clasps at the container ends, however as the polyester fiberfill fills with debris, upward pressure forces the filter media pad against the lid and it can open at the sides. I drilled small holes at the center of each side of the lid and secured it to the container with wire ties.

Step 7: Pipe Connections

The second of the two containers has a pipe cap on the end. I used unions to connect the two containers and to connect to the PVC pipe from the pump for easy disassembly.

Step 8: Results

The water remains very clear and the polyester fiberfill does not need to be changed (discarded) until the end of the season. The filter media pad is very coarse and can easily be cleaned with a hose. The picture above was taken after four months.

The back-breaking job of shoveling and washing twenty 5 gallon buckets of lava rock each Spring is now but a fading memory.

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7 Discussions


2 years ago

I also laid a brick on each corner of the support grate (below the fiberfill). As the fiberfill loads with gunk, the upward water flow tends to lift the filter box. The weight of the bricks prevents this. In addition, I secured each long side side of the lid with a wire tie mid-way, drilling a small hole through the lid and box edge. Again the upward flow of the water against the partially loaded fiberfill tends to bow the lid in the middle and lift it. I am hopeful that these two mods will allow the filters to run all season with no attention.


3 years ago

instead of lattice as the support you should be able to use grid style light defuser for a florescent light fixture. I used this style defuser to make an aquarium filter. it worked great.


3 years ago

Interesting project and very nice results. Very pretty pond. I think i will use a plastic paint(black) on the lid to my filter to hide it away in the filter pond.

1 reply

Reply 3 years ago

Not a bad idea. Maybe rough it up a bit with sandpaper first to help it stick.


3 years ago

Excellent idea and Instructable.


3 years ago

Cool instructable. Did you test the water to know that the lava rocks needed to be cleaned? Is there a way to reuse the poly-fil?

1 reply

Reply 3 years ago

Testing the water is not necessary. By the end of the season, when I remove the pump and drain the header pond, the lava rocks have become coated/filled with algae and muck. They become a solid mass by Spring. Without cleaning, the flow would be blocked and the surface area for bacterial growth greatly diminished..

Cleaning the poly-fil for reuse is virtually impossible and definitely not worth the $10, or so, annual cost.