A few weeks ago I added a 55 gallon biological barrel filter to my pond. It was pretty easy to build and fairly inexpensive. The hardest part is finding a barrel. I ended up getting one from Ebay, but you can check with your local car wash who might give you one for free as it's where the car soap comes in. My choice was to make an upflow design, as I wanted to make sure that the poop and gunk sunk to the bottom so that I could then flush it out easily.

Here is the first level of guts of the barrel. I drilled three 2" holes (buy a 2 1/4" hole saw to accomplish this). The lowest hole is for my drain; the second lowest is my intake where the water comes in from the pond; and the highest hole is the return to where the water heads to my Sequence 750 external pump. Instead of bulkhead fittings, I visited the conduit pipe section of Home Depot, and purchased 2" male and female fittings (these have better threading than the piping in the PVC section). I then fitted them together and sealed with PL Roofing and Flashing Sealant. I then put a 2" pipe in the intake pipe and put two street ells on it so the muck would come in and the water would swirl in like a vortex. This helps the heavier muck sink and lighter cleaner water rise. In the photo you can see that I've got a ball valve on the outside of the barrel. I simply open that up when I'm ready to flush the crap from the barrel.

Hint! Do not glue your PVC on the inside of the barrel, so you can fiddle with it when necessary or clean it. Of course, all the PVC on the outside of the barrel has to be primed and glued. Here it is:

Next, I built a stand from 1" pvc and elbows so that my filter media could sit on top of it without pushing down my intake:



I then dropped this into the bottom of the barrel as so:


Now go visit the lighting area of your local hardware store and head over the the aisle with the dropped ceiling material. You'll see these large recatangular grids to buy. Grab one and cut it in a circle:
 

I used the bottom of the barrel as a template and then just kept clipping the plastic with a nipper until it fit. I then placed it on top of my stand as so:



Cool. Let's move along. Next I purchased two Matala filter mats on Ebay. They were about $27 each with free shipping...a bit pricey, I know! But they will last many years. I cut both of them in a circle shape just like my plastic grid. I decided on a green and black one, as I felt the level of Matala was too fine and might clog my barrel:




Now, I pop my Matala mats on top of my stand so they sit nice and flat. You can clearly see my pink sump pit in the photo here. It sits below the barrel and is nothing more than a large rubber bucket. It has to be big enough for your sump pump to fit into. You can also see that my filter pit is pretty bare bones and has dirt walls. Nothing fancy here.





Here's my Zoeller sump pump that sits in my rubber sump bucket. Bought in on Ebay:



Finally, we cap of our return pipe with a sweep elbow:



In the remaining space on the upper portion of the barrel, you can put in whatever bio media you want. You can put bio balls in a mesh laundry bag, strapping or in my case, bacti-twist (sorry no pic of this). Here's how the whole thing looks hidden in my filter pit that is covered with a deck that I made. The panels are hinged so that I can raise them easily to maintain the equipment:



For more ideas and designs on bio or barrel filters, check out our DIY/Homemade section on Pond Mutt!