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Container Bog Filter


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  • Regular Member

Last June, I made a mini bog filter to use with my 120 gallon tub pond.


At the time I intended to make an improved, larger version. But the flimsy tote held up very well, and still works fine. However the bog filter for my back pond had an overflow problem that required me to tear it apart and do some rebuilding. So I decided to make a new container bog filter to use as a temporary filter for the back pond while I did repairs.

The container for making this filter is a muck bucket from Tractor Supply. This is a very sturdy container with a capacity of 17 gallons. While it's a little rustic to use indoors, it looks very nice outside. Incidentally, the link has a misprint. The container is 18" tall, not 28".

The first picture shows the materials I used to make the filter.


At the upper left, you see a sheet of Matala filter medium. (A source). To the right is the muck bucket. I'll introduce the plumbing pieces as they are used.

The next picture shows the tools that are needed.


You see a drill, to the right of that, a pvc pipe cutter. You don't need the pipe cutter since you can cut pvc pipe with any saw, but it makes it a lot easier. Below the cutter are two different sizes of hole saw. This is a drill attachment that allows you to cut a perfect round hole. You can get a large set of cheap hole saws that will work great on plastic and wood at Harbor Freight. I also should have included a kitchen knife, a marker, and a yard stick.

The first thing I will build is a little "stool" made of pvc pipe that will support the filter media in the filter. This requires some 1/2 inch pvc pipe and four 1/2 inch fittings, called side outlet elbows. The stool is going to sit in the bottom of the container like this:


The easiest way to determine the length of the pipe pieces is to set the fittings in the bucket in a square and measure the length of pipe required to fit them together. For this container it's about 9 1/2 inches. If you measure wrong it's no big deal. This isn't brain surgery. If the pipes turn out to be the wrong size, cut some new ones. You've got a 10 foot length of pipe.

Push the pipes into the elbows to make a square:


and check to make sure it fits in the container. Then cut some 2 inch pieces of pipe to make legs for the stool. Push them in so the (upside down) stool looks like this:


Next we will make the pipes that take the water from the pond to the bottom of the filter. Later in this thread, I will talk about how to chose the size of pipe you need. I am using 1 inch pvc for this filter. The pipe that goes from the top to the bottom of the filter will be about an inch and a half shorter than the height of the container. We attach to this two fittings called tees, so it looks like this:


At the bottom of this pipe, we will make a "swirler." We will put a piece of pipe in each side of the tee, and put elbows on each end pointing in opposite directions. The water that comes down the pipe will rotate in a "whirlpool," that will help to sediment debris. To determine how long to cut the pieces of pipe, we just put the tee in the center and the elbows on each side and measure how long the pipe needs to be to connect them. (Remember the pipe goes into the fitting.)


Cut the pieces of pvc pipe, connect them to the fittings, and we have the swirler.


The medium in this filter will be gravel, and the purpose of the stool is to support that medium. But, as you notice, the stool has no top. We need a top that will allow the water to flow upward through it and still will support the gravel. There are gratings you can use, but my favorite support is Matala filter medium. (There is a link to a source where I first mentioned this above.) It is rigid enough that when it sets on the stool it doesn't bend out of shape. It is porous enough that water flows through easily, but little gravel gets into the spaces, and it doesn't wear out. I usually use the black (coarse) Matala, to support media, but I didn't have any, so I used the green (medium) instead. I works fine too.


The diameter of the container at the height of the stool was 17 1/2 inches, so I cut a square of Matala that size.


Matala cuts easily with a serrated kitchen knife.

I marked the center, and marked equal distances from the center to make a circle. Matala compresses a bit, so it's best to cut it for a tight fit.


Then I made a hole in the center for the vertical pipe.


I made the hole too big. As I said, this material compresses, so all I had to do is cut an "X" at the center and push the pipe through. The fit was sloppy. As I also said, this isn't brain surgery. I just took some little scraps of Matala and wedged them in the space aroung the pipe to make them fit nice and snug.


So now we look at the top of the pipe to see how the water comes in. The water will come in the side arm of the tee, and then run down the pipe. We will eventually put a piece of pipe in the top opening of the tee so water doesn't spew out the top, but we will leave it open at the top. If we closed that opening, we would have a siphon from the bottom of the filter to the pump in the pond. If the pump should stop working because the electricity went off, the water would siphon from the bottom of the filter into the pond until the filter was empty and the pond had a load of crud. The opening at the top of the tee breaks the siphon so that can't happen.

The simplest (and perfectly good) design would have a pipe fitting into the side opening of the tee, and connecting to the tubing from the pump by means of a barb fitting, like this:


The hose fits on the end of the side pipe.

I decided to fancy this filter up with a venturi , which is the black thing in the second picture above. A venturi is a device for inserting air into the water stream. Air comes in that little pipe on the top of the venturi, producing a stream of tiny bubbles in the water. Those bubbles go down to the bottom of the filter producing the same effect as if you had an airstone down there.

Actually, that open top on the tee also aerates the water, but it produces big bubbles of air so your filter burps. The venturi makes it fizz.

You will notice the fittings on either side of the venturi. These are to make pipes that aren't the same size fit together. I will make a separate post later in this thread called "Making it fit," in which I will explain how you fit together different sizes of pipes and pipe to tubing/hoses.

The next thing we will do is make the spout that dumps the water back into the pond. This will be near the top of the container. The outlet pipe must be larger than the inlet pipe to keep the filter from overflowing. I have one inch inlet piping, so I will use a 1 1/2 inch outlet pipe. I will use a 1 1/2 inch uniseal to put the pipe through the side of the container. The link shows the size hole you need for each size of uniseal. For a 1 1/2 inch uniseal, we need a 2 1/2 inch hole. So I put a 2 1/2 inch hole saw on my drill.


Notice that there is a small drill bit sticking out of the middle of the hole saw. We put that in the center of our future hole, and it cuts first, anchoring the saw in place when we cut the bigger hole. So I mark the hole,


and drill it.


After drilling the hole, I use sandpaper to get a nice smooth edge. This helps to make a perfect fit with the uniseal. Also, any irregularities in the hole can make it very difficult to put the pipe throu the uniseal.

Then I push the uniseal into the hole,


and push the pipe through the uniseal.


If you look at the end of the pipe inside the bucket, you may be able to see that I took a file and beveled that end just a little. This makes it easier to push the larger pipes through the uniseal, which sometimes seems impossible. It's challenging to find a lubricant for pvc. None of the usual things -- oil, silicone, greases -- work. Some people said that there was an expensive product that Lowes used to sell that worked great, but they didn't know where to find it now. Then one DIYer found a cheap product that worked at the grocery store:


It's water soluble and nontoxic. Just put some on the end of the pipe and it goes in easily.

Once the pipe is through the uniseal you can push it in or out as you wish, particularly if it is lubricated.

In the second picture up, you may have noticed another hole near the bottom of the bucket. This hole is for the dump valve -- a "faucet" at the bottom of the filter for flushing the filter. Seen again here:


It is sized to take a 3/4 inch uniseal. Here are the pices needed for this valve:


At the top you see the valve I am using, a 3/4 inch quarter turn valve. You can use a hose bibb of any type. Below that, from left to right, a piece of 3/4 " pipe, a 3/4 inch uniseal, and a 3/4 inch elbow. Below that you see an adaptor that will connect the valve to the pipe. The tape is teflon tape that is used to seal the threaded connections. I wrapped the tape around the threads of the adaptor


and screw it into the valve.


I put the uniseal in the hole


and push the pipe through the uniseal.


On the outside, I push the adaptoronto the pipe.


I want the dump valve to empty the bucket completely, so I put an elbow and a piece of pvc, long enough to reach to the bottom, on the pipe on the inside.



The internal plumbing is now complete.


I put in the Matala and am ready to fill the filter, once I prepare a place for it.


The pond sides are just over a foot above ground level, so I will have to raise the filter. First I have to level the ground. I use some fine gravel.


I put a patio block on the leveled gravel and make sure that is level.


It's not high enough, so I use some half-high cement blocks,


and top those with some more patio blocks,


which makes it more than high enough.


Note that this is a temporary filter location, or I would make some effort to make the base prettier.

Notice the dump valve is in position where I can put a hose on it and run the hose out to the lawn.


I decided to try having the outlet pipe go to the bottom of the pond and direct the flow toward the pump, to see if this would "sweep the bottom of the pond. So I made an extension for the outspout:


I got out my spray paint and made the visible pipes black, and attached the hose from the pump to the inlet pipe.


In the picture above, you see the bog filter that belongs to the pond right behind the container filter. I'll be removing that gravel and using some of it in the new filter. Notice there's a black pipe with a white end coming out of the bog. Right above it you see a corrugated hose with an elbow on it attached to the inlet pipe to the container filter. That elbow came off the white end of the inlet pipe to the pond bog filter. The ungainly plumbing is only because this is a temporary set up. It's perfectly serviceable though.

You can see it better here:


So I took the plants out of the bog, and I dug out gravel, some of which went into the container bog.


When I got the gravel up near the outlet pipe, I decided to fit this dollar store basket over the end of the pipe. I will put a piece of Matala in it, and the purpose will be to keep the gravel out of the outlet pipe. I cut a hole in the end of the basket for the pipe.


Oh look, the basket changed color! I broke the first one trying to cut a hole. Actually, I broke the second one too, but it held together well enough to make it work.

The first plants I put in were some rain lilies from the disassembled pond bog. I put in some stevia from that bog, dill, boxwood basil, and lemon thyme.


I pulled out some of the rain lilies and put them in another filter, and dug up some nasturtiums from a garden plot and put them in.


Once I got the filter filled with gravel, it was pretty pretty muddy. I turned the pump on to fill the filter, turned it off and drained the dirty water with a hose attached to the dump valve.


When I turned on the pump, water splashed out of the top tee, even when I put a short pipe in it.


A longer pipe kept the water in place, but look at all the bubbles.


The water in the pond got pretty murky with all the mud associated with the plants.




Look at all the bubbles coming up through the gravel from the venturi. Click on it to start the video. I don't know how to do this right.


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  • Regular Member

Love it! I was actually going to start building a bog filter with a 2500 gph (est) pump from harbor freight for my 125 gallon so I can run it even if it rains (can't do that with my penguins). I was planning on a butterfly plant mini garden. Can any plant go in the top, or do some plants require soil rather than gravel? I just love these. I'm sure ill never buy a filter again! (Maybe just a canister... Maybe....)

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  • Regular Member

Most plants can grow in a bog filter. The reason why many plants can't grow in water is that their roots don't get enough oxygen. The bog filter provides a stream of aerated water over the roots which keeps the plant happy.

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  • 1 year later...
  • Regular Member

I was disappointed with the plant growth in this filter. While it was good initially, plant growth decreased with time. I suspect this was because the gravel was compacting and this affected the plant roots. I decided to replace most of the gravel with a lighter growth medium. I used this hydroponics/aquaponics medium.

The results were amazing The size of the plants easily quadrupled in the next few months. Gravel is cheap, but I won't be using it in a container bog filter again. Actually, I like this medium even better.

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