Pond Mechanical and Biological Waterfall Filter

I own a 200 to 250 gallon round pond in the yard and every summer it turns green with algae. This year I decided to build a water filter that would solve this problem. My objective was to make a biological and mechanical filter that was easy to clean and wanted the filtering material to be easy to access. So this is what I came up with.

Here is a diagram and a video of the pond filter in simulated action.

The water comes into the filter through the bottom, forced through the bio-balls and then up and through the other filters and then out through the waterfall into the pond.

I started off my purchasing two storage bins (one inside the other) and a dish drying rack from the local hardware store. The dish drying rack was basically to hold the bio balls from floating way and also to act as a pedestal for the filter tray assembly to sit on.

The large bin for the outside of the filter. (seen in grey plastic and outlined in yellow)

The smaller bin that fits inside the filter. (seen in clear plastic and outline in red

The dish drying tray. (seen in white plastic and outlined in green)

I then cut a rectangular hole out of the back of the smaller plastic bin so the water could enter into the mechanical part of the filter.

On the underside of the large bin container, I drilled a two inch hole for the drainage pipe. I bought a sheet of rubber gasket material and I manually cut a gasket that fit around the hole to stop any leakage between the bin and the valve pipe. I assembled the PVP valve, a few short pieces of straight PVC and a PVC elbow to create the drainage valve. I added the gasket and ran the threaded PVC through the large bin container hole and tightened the parts together. I did not need to glue any of the PVC parts together because the water pressure is very low.

I bought a pump and pump box from Amazon which included some piping. I drilled a half inch hole in the underside of the large container bin and cut another gasket out of the gasket material. I used two threaded PVC connectors and attached the assembly to the large bin container hole with the gasket.

I formed a piece of sheet metal in the shape of a waterfall pan assembly. Then I cut a notch in the large bin container a few inches below the top on the large bin edge so the metal waterfall pan will be below the water line of the filter.

I had some old plastic shelving so I create a tray to hold the individual filtering materials. This entire rack sits on the floor of the smaller bin container. Luckily the filter material did not float so placing the filtering material in the slots can easily added to the each slot.

I attached the two bins with a home made bolt mount. I made this piece out of thick plastic and drilled two holes into the bolt mount plastic and through the two bins. I connect the two bins together with toilet seat bolts that can be bought separately from the seats. The bolts are long and rust resistant. They also have a rubber washer that seals the holes. I took some 100 percent silicone caulking and ran a thick bead of caulk between the two bins then ran the toilet seat bolts through them both and synched the bolts down.

I drilled two more holes through both bins, the bolt mount and the metal waterfall tray to connect the waterfall tray assembly. I ran a thick bead of silicone under the waterfall metal tray and along the connection points of the bins. Then I synched the entire assembly together. I added a few self tapping metal screws through the waterfall metal into the bolt mount to secure the waterfall tray. Then I let all the silicone dry completely. It usually takes about 24 hours.

Finally I added the bio balls and some bio tubes cut from plastic electrical conduit. The smaller plastic bin wants to float when water is added so I installed a small purple bungee cord to the back of the smaller plastic bin to hold it down.

I built a wooden cedar box from fencing pickets, stained and seal it for water resistance. Then I connected the water pump and added the filtering material that I bought from EBay.

Important note: I had to lean the entire filter assembly slightly forward towards the pond so to encourage the water to flow towards the pond. If the filters does clog up over time, this also encourages the water to flow back into the pond and not onto the ground thus draining the your pond of water.