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Mini Bog Filter for Aquarium or Container Pond


shakaho

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I recently completed a bog filter for my back pond: http://www.kokosgold...-the-back-pond/ But before I built it, I made a small bog filter in a container for My 120 gallon tub pond. In part, I made it to find any potential problems with building a bigger bog. But I also wanted a bog filter for this tub, and wanted to use it as a prototype for a pretty bog filter for indoors. This one is strictly utilitarian.

Basically a bog filter is a container of gravel -- ideally 1 foot deep -- with plants growing in the top. The gravel is the filter medium. Water from the tank or pond is pumped to the bottom of the bog, percolates up through the gravel, and is dumped back into the pond/tank. The gravel provides both mechanical filtration and biofiltration. Particles in the water stick to gravel pebbles near the bottom of the bog where they are devoured by a huge variety of microorganisms. Their waste products serve as food for other microorganisms. And don't forget the plants! Their roots will spread through the gravel -- particularly the upper levels -- and slurp up all the nutrients they need. You won't find any nitrates in a tank filtered by a bog.

The plants you can grow in the top of a bog filter are limited primarily by the light available. Outdoors, you can grow almost any garden plant in a bog filter, indoors you can do the same if you have good grow lights. Otherwise, you can grow almost any houseplant. You are not limited to "bog plants." A bog plant or marginal plant is adapted for growing with its roots under water. Specifically, the roots can live in an anaerobic environment. When a regular land plant dies when the soil becomes and remains waterlogged, it isn't because the roots don't like water, it's because they aren't getting enough oxygen from the water or waterlogged soil.

The water in the bog filter comes from your oxygenated tank/pond (and there are ways you can aerate it further). Thus plants that normally grow in moist soil are perfectly happy in a bog filter.

My first mistake was in the container I chose -- a cheap tote from Home Depot. It had the depth I wanted (~ 15 inches), but the material was so flimsy that not only did it distort from the water pressure as expected, but I had to reinforce the wall to put a pipe through it.

What would I get instead? Basically something that's designed to hold water, soil, or other heavy material. For an indoor tank, a pretty, large flowerpot or urn is perfect. You want: plastic/resin/fiberglass, no holes in the bottom, a large surface area for planting, a height of 12-20 inches, a sturdy material that doesn't deform easily, and a surface that doesn't have lumps and bumps where you want to put your out spout (near the top) and your clean out valve.(near the bottom). After that, what matters is how well it fits your decor. The volume of the container should be at least 10% of the tank volume.

Outdoors, for an in-ground pond of up to 500 gallons, you can't beat a 50 gallon Rubbermaid stock tank.http://www.tractorsu...apacity-2229927. It's the right depth, has huge surface area, and is super tough. It's also ugly, but you can hide it. The bog container only has to be high enough so a spout from it goes over the edge of the pond, so you can sink it in the ground and put something around the sides (even soil) to make it disappear. For a somewhat smaller pond, the Tuff Stuff 25 or 40 gallon stock tanks are great and inexpensive: http://www.tractorsu...40-gal--2229846. Of course you can use large flowerpots for smaller ponds.

I started out by putting in the spout.

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You see the tote, with a red mark where I want the spout; a drill equipped with a hole saw, and the little black piece by the drill -- a uniseal. http://www.aussieglo...om/uniseal1.htm I used a 1 inch pipe as the out spout. While it worked, if I did it over I would go up to 1 1/2 inches.

I drilled the hole in the tote,

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and pushed in the uniseal.

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All I have to do is push in the 1 inch pvc pipe to finish the out spout, but I will do that later.

Next, I make a "stool" to support the media. I used 1/2 in pvc pipe, four side outlet elbows http://www.lowes.com...product_price|0 and three t-fittings: http://www.lowes.com...product_price|0 The stool is only about 3 inches tall. It fits in the tote:

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Here is the plumbing that takes the water to the bottom of the tote:

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The black pipe at the upper right receives the water from the pump. Tubing will connect the pump in the tank/pond to this pipe. The pipe is black only because it was recycled from an old pond cover that I had painted black.

This pipe fits into a T-fitting, where the water will go down to the bottom of the filter. The little piece of pipe at the top is there because some of the water will bubble up a little ways before it goes down. This is to keep it in the pipe. The turbulence at this corner catches some air, and aerating a filter is a good thing. When the water gets to the bottom of the pipe, another T-fitting splits it into two pipes. I put an elbow on those piles to make the water swirl around the bottom of the filter. This is probably totally unnecessary, but I like swirlers.

Here's the swirler and stool in the tote.

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I want open water at the bottom of the filter so all parts of the bog are likely to get the same quality of water. This is why I made the stool to hold a support for the gravel. I used coarse Matala http://www.drsfoster...fm?pcatid=15799 for the support. I cut a hole in the center of the Matala -- which you can sort of see -- for the pipe to go through.

Here's the Matala in the tote. I have spray painted the visible part of the plumbing black.

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If you look at the end of of the side pipe, you will see that I added some fittings. The first is an adapter like this one: http://www.homedepot...1&storeId=10051 . The end on the left slips on over the pipe. The end at the right has female threads so you can screw a male fitting into it. The male fitting is a barb fitting like this: http://www.homedepot..._-202721873-_-N . The barb on the left in this picture is where the tubing from the pump goes on. The other end screws into the adapter.

If you are going to connect a pvc pipe to tubing, the way to get it right is to take the pipe and the tubing to your hardware store, home improvement store, or plumbing store and say, "I want to connect this to this. What do I need?" If the sales person acts confused, ask for the person who knows. These departments are very badly organized. I've spent a very long time looking for a fitting when I knew exactly what I wanted.

The next picture shows some additional plumbing. At the top right, you can see the out spout, 1 inch pvc pipe which is simply pushed (very hard) into the uniseal. I pushed it through far enough so I could put an elbow on it. The elbow twists on the pipe so I can adjust the level to which the water fills the tote. The black thing on the elbow is a strainer which I thought would keep the gravel out of the spout. When I actually used it, it clogged almost immediately, so it was discarded.

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If you look at the outside of the tote, you see a red handle. That is for the dump valve which is a 1 inch ball valve like this: http://www.homedepot...e&storeId=10051 I painted the white part black for appearance. This valve slips onto a 1 inch pipe, which goes through the wall of the tote using another uniseal. But a problem arose. The wall of this cheap tote was so flimsy, that this heavier fitting distorted the wall enough to make a leak around the uniseal. This is why I said in the introduction to use a container designed to hold water and/or soil. So I reinforced the wall of the tote.

If you look inside the tote, starting at the wall you see a thin red line, a black thing, and then a white end.

The white is the pvc pipe. The black is the uniseal. And the red is a piece of a flexible cutting board: http://www.ikea.com/...ucts/50153123/# I cut a hole in this for the uniseal, pushed the uniseal through both the tote and the red piece, pushed the pipe in, and tested. NO leak!

The next step I should have done is make a "collar" for the tote out of 1x3 lumber. The weight of the water and gravel will try to turn the rectangular tote into a circular tub. I actually cut the boards for it, but wanted to wait for my husband to get home to help put it together, which really works better with two people.

You can see the collar in this picture:

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It's not pretty, and you don't need it if you get a good flowerpot, stock tank, or other sturdy container.

So I started washing and adding gravel. I started with some river stones to keep the smaller pea gravel from clogging the holes in the Matala.

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Then I added pea gravel and plants. Notice that I put the whole root ball in the gravel without washing. The plants need some soil to get started. It won't come up through the gravel. Soil and compost is an excellent source of nitrifying bacteria as well. Instant cycle. The bungee cord didn't do too well at holding to tote in shape.

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Once I got the bog planted, I had to try it out, so I hooked up the pump.

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The pump is at the opposite end of the tank from the filter. The hose goes from the pump to the filter.

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The hose attaches to that barb fitting. You also can see a small rectangle of black Matala with a white thing in the center. The white is the elbow fitting. When I first turned on the pump, the gravel flowed into the elbow and out the spout into the tank. So I made the little filter barrier. It works perfectly.

When my husband got home, we drained the water from the filter using that nice ball valve, and put on the collar. He grumbled a lot about how this should have been done when the tote was empty and I cut the boards wrong, both of which were true, but we got it together.

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The filter works well and the plants have grown a lot. I'm going to set up a bog filter in a pretty flowerpot for an indoor tank, but right now all the fishies are outside.

Anyone who has nitrate in their tap water should make use of a bog filter. You can use it for pretreatment of the water or use it for the tank. The nitrates will be gone.

I have described a couple of other small filters in other posts. If you are planning to build a filter, you might want to look at those as well. The basic principles of filter constructions are the same in all of them.

http://www.kokosgold...e-instant-pond/

http://www.kokosgold...em-for-the-40b/

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Very nice, shakaho. I think I'm going to make one for each of my tanks. The only thing is that I will convert the output into spray bars. The splashing noise otherwise will kill me. :)

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I can't stand splashing either. What I do outside is have a basket of lava rock (with plants in it, of course) right under the out spout, so that the water pours onto the rock. This silences it completely, while adding a little extra filtration.

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In the second picture I had just added sand and was using quilt batting to clear the water.

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Another great project w/ explicit instructions,Shakaho :clapping: I am going to make 1 of these for my pond-soon. Thank you so much for your explanations and pictures :)

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You know, after spending 6 to 8 hours describing a project, it's really great to hear that someone is planning to take advantage of it. As a biologist, it is obvious to me that a bog filter will give optimum biofiltration, since a bog filter is basically an artificial wetland and wetlands are the most important ecosystems in water purification. What surprised me was how simple it was to build one.

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Here are some current pictures of the mini bog filter and the pond it serves. The bog filter is on the left. You can see the dark tote sitting on a light cement patio block, but it blends in pretty well.

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As you can see, the plants have grown a lot.

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You should look into the larger Tuff Stuff stock tanks. They are lighter and cheaper than the Rubbermaid tanks and are a better shape with more surface area.

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I definitely will! The space I have for it is about 3 ft by 6ft at the very most, so I'm planning on getting the biggest tank I can fit. The only thing I am worried about is I won't be able to dig at all to have it partially submerged, and while it is decently shaded, it does get in the 100's sometimes. Do you think this will be an issue? I plan on having a fountain pump in it to help cool as much as possible.

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Here's some info on the tanks: http://www.tufftubs.com/htdocs/plinoval.htm If you have shade, it will be fine. If your 24 hour lows and highs were 70-100 degrees for the air, the range for a tank of water would be about 80-90. Goldfish are fine in that temperature range. Aeration is a good idea though, since the warmer the water the less oxygen it will hold.

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Recently it's been in the high 50's at night and high 80's/low 90's during the day. A few weeks ago it got up to 105 though but it's not that warm very often. I'm thinking I could try to insulate the pond somehow possibly.. I'll have to brainstorm. Thank you for your help and I'll make another post with all my pond questions/concerns when I have a chance. :)

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I would expect if you had a 150 gallon pond and checked the temperature of the water, it would be in the70 in the morning and get up to about 80 in late afternoon. Those are excellent temperatures for goldfish.

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  • 6 months later...
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Just a couple of comments on this filter after six months of operation.

The flimsy tote has held up better than I expected. I have drained it and moved it a few times. Each time I expected a leak, and each time it stayed intact. Nevertheless, I am going to build the next one with one of these. They are sturdy, look good, and are very inexpensive for the quality, They aren't 28 inches high as the link says, but actually 18 inches.

Making a support for the gravel so there is open water underneath is a very good idea, and one I will continue to use.

You don't need much gravel depth and should not fill the gravel to the top. As the plants grow their roots will need space and will push the gravel up. I started with the idea that the gravel should end 2 inches below the top. Experience says 4 inches. :)

For the same reason, I learned to curb my enthusiasm for adding plants. One large plant or a few small ones will work fine.

This is a very good filter. Since filter medium is probably the biggest expense in making a filter, it's also about the cheapest you can make.

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  • 2 weeks later...
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What's it made of? I know you can drill holes in a ceramic pot (at least that others have done it) but I've never tried it. You may need a special hole saw for that. "Resin" is functionally the same as plastic.

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I'm really formulating a plan to do this indoors, but I can't seem to figure out a way to hoist the big decorative pot above the tank.

I wonder if there's a way to get the water to flow to a lower part of the bog, and be sucked back into the tank by another pond pump?

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What size tank do you have and what kind of stand? Do you have space at one end of the tank for a supporting structure? In other words, pictures please -- of the tank, location and the pot. Remember, only the spout has to be higher than the top of the tank.

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I have the same as you, a petco special 40breeder. It's on a very, very sturdy coffee table, but I don't know if I'd trust it holding another 100 plus pounds. There isn't much extra room on the stand anyway.

I may be able to find a garage sale night stand, and put a big pot on top of that. What happens if the pot ends up being more than 10% of the tank volume? Does that cause problems for the system?

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That's so smart! I was thinking something like a barstool, actually. I'd have to bolt it either to the wall, or to the ground though. Either my son, or the cat would be knocking it over daily. I really want to try this, so I'm going to have to save my pennies. Big, pretty, pots are expensive! I imagine it's tough finding them without a hole in the bottom. I was looking through walmart's clearance pots just this evening, and all the big ones, even the heavy ceramic looking ones, had big fat drainage holes.

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