Bog Filtration Questions Answered

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Duck Pond Bog Blog

We recently received two questions on a previous blog: BOG FILTRATION, THE PERFECT COMPLEMENT TO BIOLOGICAL FILTERS. The questions had similar answers so we are sharing them in a new blog. First question:

Have you had (or heard of) much success with using bog filters in small duck ponds? I like the idea of using both bio and bog (would help with the extra muck) but not sure if ducks would tear the bog filter’s plants up. Ideally I would set one up with 4-5 ducks in mind.

Location

Your choices will be determined by what grows best in your area. You will want to get an aggressive grower(s) in there to convert all that stuff into easy-to-prune leaves. You may need to cut the plant matter back hard, maybe more than once a year depending on your location. Figure on a complete removal with new plant material after 5 years. That will reinvigorate and refresh the appearance of the bog.

Because the roots of aggressive growers can sometimes penetrate liner, I’d cover the excavation with underlayment, set the liner then cover that with another layer of underlayment.

Bog Size

You will want a bog that’s at least 30% of the square footage of the water’s surface. That may sound excessive, but 30% is what you need for koi, and ducks are messier. Don’t hesitate to go bigger if you can. For easy maintenance, I keep my bogs shallow, but you’ll need some depth to resist the ducks. I’d probably use 8” of ¾” round gravel, which is the least costly where I live. Make sure water passes through the bed, whatever choice you make.

One last design detail that might help if you can implement it. To start the bog, I’ll set (or bury, if the bog is cut into a natural slope) a line of Eco-blox water matrix blocks 6-12” higher than water level at the head of the bog. The Eco-blox act as a settling chamber. Water entering the blocks from one side dumps all its heavy solids before passing out the top of the blocks through a layer of gravel. The water then works its way through the 8” deep gravel bed where roots remove nutrients every inch of the way back to the pond. A drain on the opposite side of the Eco-blox chamber can be opened to flush out the debris every year or two. See above drawing

The Aviary

Finally, the perimeter bog is keeping the pond in the Butterfly House crystal clear, even after 1 year with no additional filtration. Bbutterflies are easy. The photos of the pond in the Aviary, with the same system, has had issues with the ducks, geese and swans, that trifecta of vicious veggievores, devouring 80% of the bog plants.

The good news is, they only obliterated 8 of the 10 species planted. The other two, a dwarf variegated Schefflera-looking shrub and the native Purple Wandering Jew, Tradescantia pallida, are doing a pretty good job. See the rock 3’ down in the pale green water? Not bad considering there are 200 birds in there.

Consult the “Black List” of banned plants in your state before you decide on the plantings. I entered “blacklisted aquatic plants official NY” and Google returned the list for my state. Then compare that to a search for ‘Plants That Ducks Don’t Eat’ for your state. Good Luck with your duck pond!

Second Question

Hello Demi, thank you for your suggestion and answering back so quickly. Yes, Im certainly going to use 45ml epdm rubber liner. ( That was a typo). I think I got the concept. All though my existing pond had a high 3′ waterfall w/no stream.. Reading your instructions I will incorporate a stream leading into the pond. Would I still install a deep and wide stream bed with 3-5 inches of gravel in the stream or on top of the Eco-blox? (A little confused) My pump is plumbed with a 2″ Sch40 flex pipe.

So would I install a “T” at the pump with the same 2″ flex pipe but one leading up to the bio-falls filter and the other leading (connecting) to the eco-box? Once the 2″ flex pipe is connected to the inlet of the eco-box does water fill the box and passes through the rock, gravel and aquatic plants and then down into the stream? Does the Waterfall filter come out somewhere else into the stream? I get the drawing and the concept but not sure about the waterfall filter? I would still have spring flo media and filter-mat in the waterfall filter but no filter-mat in the skimmer. Correct?

Thought if you can be so kind is to draw another picture with the waterfall and bio-bog. Thanks for giving me such great advise. Can’t wait to get the pond rebuilt. But this time with a better out come. You really made some good points.

Perimeter Bog with Eco-Blox Settling Chamber

Hi again! This response required a sketch, which I’m bad at, so it took longer to reply than just text would have. To answer your questions in order: If you have the biofilter at the edge of the pond with the water flowing down a 3’ waterfall directly in front of it, keep it that way. Put the bog somewhere else along the perimeter, anywhere lush plantings will be appreciated and you can easily get to for pruning. The reason I included a stream is because I thought you had one.

Perimeter Bog

A perimeter bog like the one sketched can be placed anywhere, at any distance from the pond including right next to it, as pictured. It can also sit as high or low as you like, as long as water pumped into it will flow back into the pond. The sketch shows water flowing over the rock, but it could just as well flow around it. The bog works equally well whether you see the water coming back in as a little waterfall, or water seeps back in invisibly.

You won’t need the mat in the Skimmer because you will have effectively doubled your filtration and increased your ammonia and nitrate removal capacity. Don’t forget to add a valve to control the water going in to the bog. Don’t worry about a valve on the biofilter side. Because the bog is so much lower, the water will all go towards that lowest path of least resistance. Shutting the valve to the bog to about ¾ closed will direct a quarter of the volume into the bog, and shunt the rest of the water up to the filter.

AWG University

For more detailed information about bogs in general, check out Atlantic Water Gardens University, Natural Filtration 301: https://www.atlanticwatergardens.com/university/courses/natural-filtration-301

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