How to Make a Pond Biofilter: Part One

The subtitle of this entry is My Mother the Guinea Pig. I couldn't resist... though it's actually my mother's pond that is the guinea pig. Here's why. When I first wrote that I was building a small pond and mentioned I was just planning to use a submersible pump for water circulation, the word 'biofilter' was quickly whispered in my e-ear (thank you for your emails!), by other pond owners who know the preventative benefit of the continual filtering of pond gunk. I admit I had a few dizzying days where I was trying to figure out what the best biofilter setup for my pond would be. Surfing for trustworthy pond information is a dangerous affair. There is reams and reams of contradictory advice out there. And there's some really questionable sites where they brag about how cheaply you can make your own biofilter and then offer to sell you the five bags of sponges you'll need for a mere $29 per bag. As if. Not for the faint of heart/confused/ignorant/frugal like me. Finally, I stumbled upon a post somewhere about creating biofilters from basic household supplies, which you'll see below. I think my luck was formed after looking at some commercial filters in the local home and garden shops and seeing the ridiculous price tags: $50-$100 for a plastic box with some sponges in it and two holes for water intake and output. Ding! Ding! Ding! A plastic box with some sponges in it and two holes for water intake and output. Ding! Ding! Ding! Now I can do that myself. This is where the guinea pig part comes in. Most conveniently, my beloved mother's pond happens to be a profound version of pea soup right now. While there's algae there, a lot of the problem seems to be murky muck. That's my diagnosis anyways. So, I thought I would make her a biofilter and see how it performs. I'll work out any kinks based on that and then rig one up for my pond. Here we go. This is my mother's pond. Beautiful and entertaining with some fish and Esther the frog. Despite the thickness of the water, there is life in there.

Supply List For the Biofilter: -one small rubbermaid tub with a well-fitting lid ($6) -a few bags of various kitchen sponges and scrubber pads at the dollar store ($4) -one mesh laundry bag to hold the sponges ($1) -one brick -a piece of wire mesh -one section of vacuum cleaner hose -submersible pump with half the flow rate of the pond volume Tools: electric drill and keyhole bit for water hose openings

Here's What I Did: I drilled a hole for the water intake (lower right side of box), just slightly bigger than the output hose from the pump. My mom's pond is about 150 gallons so the pump should only run half that rate (75 gph). Apparently if it's too fast, the sponges in the filter can't adequately catch the gunk. Conveniently, she has two pumps and I used the slower one for the biofilter.

I found this vacuum cleaner hose attachment in someone's garbage yesterday and it works perfectly as an output hose. I wrapped some bubble wrap around the vac hose to tightly fill in any gaps at the tub opening so it wouldn't leak. The output hose is situated lower than the water intake hose and has to be twice as wide an opening. You do not want your biofilter container to overflow so a wider output opening allows good outflow.

I put a brick in the bottom to create a gap for water below the gunk-collecting sponges. I noticed after a test run that a bunch of mud gathered on the bottom right away. That's good. Any muck the filter pulls from the pond is a good thing. Just ask the fish.

The wire mesh helps create a division between the sponges and the water reservoir in the bottom:

I put in as many sponges and scrubbies as I could comfortably fit in the bag. I used the mesh laundry bag so I could easily pull out the sponges if need be:

Put a lid on it, will you? I know some people have open biofilters and some put plants in them, but for now, this baby is having a lid so I can hide it in the rocks surrounding mom's pond. I have more inventive ideas running through my mind but first I want to see how this works. (I'm waiting for my guinea piglet mom to give me the day two report as I write this.)

At this point I gave it another test run. I had forgotten to tuck the input hose into the mesh laundry bag and that caused some water to spill out the top of the bin. A quick adjustment (anchoring the input hose inside the mesh bag to aim it down into the bin) and it was working fine.

Here's the biofilter hidden in the rocks. The fish immediately came over to play in the waterfall:

I'm hoping as soon as today (Day Two) we will start seeing a noticeable difference in the water quality. And if we don't? Well, we'll wait some more. Stay tuned. Update-Next Day Some people say their biofilters cleared up their ponds in a matter of days, others say it takes weeks. I'm guessing with my mom's pond conditions shown here that it will take a few weeks to really clear things up. I noticed yesterday when I went over to have a look that I could see about 3-4 inches deeper into the pond than I could on day one, so that's a good sign. Filter Update I added a mechanical filter using polyester quilt batting to clear the water up faster. You can read about it here.

Related Entries: All pond related entries are listed here. The 2006 Blooming Cycle - my attempt to record blooming times. There's a complete listing of my virtual garden tours here I keep track of garden weirdness here See my garden art/junk. Do you have a picture to add to the Garden Shed Hall of Fame? Mirrors in the garden? Don't they break?