What is the correct way to build a bog filter and are there substitutes for bog filter media?


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From my research i have come across differing opinions on what is the right and the wrong way to build a bog filter. I am thoroughly confused on the matter and would hope someone would be able to give me a quick rundown of the major pitfalls to avoid and helpful tips.

I have constructed a pond that is 15 feet by 15 with a maximum depth of 7 feet in the center. I have dug down to a layer of thick blue-white clay and I am in the process of shaping the sides. It is a labor intensive process because we live on a hill but there is considerable ground water/ground seepage. During the digging process I left a 4 foot ledge which I have built up and sealed with a liner. My intention was to use this section, along with planting the edges, to filter the water. There will be no fish swimming, just me during the hot Florida summers.

I would like to begin building the bog filter but I want to do it right the first time. The filter is 3 feet wide by 15 feet long. The depth of the water in the bog is 14 inches. I plan on pumping water from the far end of the pool, and into the filter through a series of pipes with perforations which will be laid at the bottom. I think i have the general idea down but here is where I run into some issues.

The suggested rock for the filter is 3/4 inch pea gravel. This is mandatory to some but other people have found success using lava rock or other substitutes. My issue with this is there are no suppliers of pea gravel locally except for home improvement warehouses and I find their prices too high. Could i substitute a layer of bulkier rock at the bottom or a different similarly sized rock altogether (i.e. Tahitian Granite, River Rock)? I plan on putting river rock or granite in the pond bottom to prevent cloudiness and could get a discount by buying in bulk.

In addition, I am confused about the level of the water in the bog filter. Should there be some water over the gravel, lots of water, or no water at all?
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I have a hard time believing that pea gravel is unavailable, I think some employee is saying you can't get it, when he/she really means we will not get it or tell you who can. Try talking to somebody at a ready-mix concrete company, my guess is they either have it for sale or know how does. The search term"construction aggregate" or "aggregate" may work better, Pea gravel specific product and is used in construction too much to be simply unavailble. With a 3 X 15 you're talking about 1 2/3 cubic yards or about 4500-5000 lbs.

Another thing I've noticed is there are a lot of hydroponics suppliers popping up all over and what the 420ers are using to grow their products isn't really much different from our bog filters, so they maybe a resource for growing mediums and substrates
 
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I'm going to assume that you are going to line your pond with liner.

The problem with filling bog is the rock can be sharp and puncture the liner. You can use river rocks, that's what I used. the smallest size though. Or mix together. You can also use lava rock, just not at the bottom (sharp). Plants probably so better with smaller rocks for roots to hold.

I go tmine bulk from landscaping company that sell topsoil or mulch. You would have to have a truck or trailer or they have to deliver it to you. When I need a bit more i just buy it by the small bags from Home Depot.
 
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Thank you so much this is exactly what i was looking for. I thought the same thing, if the product is everywhere someone has to have it, but the place i called specializes in landscaping rock which may be the reason they suggested something different.

Thank you again for clarifying it and pointing me in the right direction.
 
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Need clarification on one point. Is this going to be a earthen-bottom or lined pond?
The bog filter is lined. I plan on the pond portion being earthen bottom. The entire bottom is solid clay for as far as i was able to dig.
 

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The bog filter is lined. I plan on the pond portion being earthen bottom. The entire bottom is solid clay for as far as i was able to dig.
I suspected as much. I would be very exacting in setting up the plumbing for this venture. The pump or pump intake must be raised to a sufficient height above the pond's bottom or you will quickly fill your "bog" with clay/soil. Adding gravel to the bottom of this pond is only a waste of money as it will eventually settle into the bottom and may prevent turbidity but for only a short period of time. You might want to re-think leaving this as an earthen-bottom pond.
 
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Thank you. While searching i found this thread in which you posted an explanation - https://www.gardenpondforum.com/threads/new-bog-in-the-neighborhood.18375/

I am prone to making decisions while doing just enough research to support my wild notions so i appreciate your expertise and advice; i fear I may have gone too far with my plan without enough forethought.

It is my understanding now that the bog would quickly fill with sediment because of the amount of suspended solids in the water, correct? This would require cleaning out of the pipes and the gravel bed on a near constant basis due to the sheer amount of water being passed through the system. Lining the pond is an option but the intial investment is the main deterrent when compared to the piecemeal construction I am accustomed to. So I am at a point when i need to consider all options before proceeding.

If my ultimate goal is to increase water clarity and, for lack of a better word, health, what are my options if i proceed with an earthen bottom pond? Could I use the "bog" with the pipes on top of the gravel and still see some natural filtration from the plants? Maybe a fountain or waterfall into the gravel bed to increase aeration? I am unsure and just spitballing here.

I have already built the "bog" pond above the main pond, so i would like to utilize it rather than rip it out. I would also like to avoid the cost of purchasing a liner for the pond. Is there a way to naturally filter my giant hole full of water, is it even possible, feasible?

I sincerely appreciate your help with this. Thank you.
 
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Would limestone gravel be ok or would that affect the ph balancd of the pond?
 
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I dont know other way. But I think since you do not want to have fish in, may be you can use some type of tarp / poster fabric (thin) just to line the pond. That will be cheaper and easier to still have bog to help with sediment. Bog is not very good at cleaning out sediment, though, especially the fine particle. The only thing that's good is something like quilt batting. in the bog, the gravel leave large enough holes for any fine things to pass through.
 
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Meyer Jordan

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Is there a way to naturally filter my giant hole full of water, is it even possible, feasible?
If your goal is water clarity, then you need to line the pond. Any mechanical filtration that would provide the desired clarity would be very labor intensive and really not practical. If you are looking to control water-borne pathogens a "bog" of the proposed size will provide absolutely no protection. If you want to utilize the already dug area for planting, fill it in with dirt and use surface flow.
 
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Awesome, so the liner is key if i want clarity. I will look for inexpensive liner solutions that other have suggested in other threads. You're comment about my bog not being the right size to reduce pathogens piqued my interest. When i have installed the liner, will the bog still be useless in that regard because it is too small? I read that 10 to 15 % is adequate with no fish present. Do you have another recommendation for reducing pathogens that might be applicable to my situation?

It is really great to be able to pick your brain. Youre very knowledgable and helpful. Thank you again.
 

Meyer Jordan

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A pond used for swimming will require the same disinfection as a commercially built swimming pool. This means, if you are really looking at protection, you have limited options. Your choices for adequate disinfection are Chlorine, commercial sized UV sterilizer, Ozone injection, and/or absolute 1 micron membrane filtration.
Wetlands (bogs) that are constructed to 'polish' filter Waste Water (sewage/storm run-off) do provide a certain level of pathogen reduction, but these sites are measured in acres and maintain a very low flow rate to allow natural predation. It has been shown that E. coli bacteria levels can be reduced to almost zero by certain zoo-plankton in a controlled environment in 48 hours. In a real life environment this predation rate may be quite different.
This leads back to your real options. All would require a certain level of maintenance and some are quite expensive.
 

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"Awesome, so the liner is key if i want clarity. I will look for inexpensive liner solutions that other have suggested in other threads."
________________________________________________________________________________

In any project, if you're going to go the time and the expense to create something, don't skimp on the basic elements for successful completion.

Going for the "inexpensive liner" may very well save you a couple of hundred bucks, but replacing it will cost you many hours of labor, plus the cost of either using another cheap liner (in which case you're right back to where you started), or buying what you should have bought in the first place, proper liner.

45mil EPDM.
 
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Agreed. Some have suggested asking roofing companies or local farms/hydroponics operations for assistance as a way to reduce costs. Our liner for our tilapia pond was leftover from a locally manmade reservoir. I never want to pay full price for anything i can get for less is all. Dont worry, 45 mil epdm is what ill use once i find that deal im looking for.

I guess the appeal for me was the natural element of the earthenbottom pond. (And the perceived ease of construction.) But with everybodys input it seems that a liner would make the most sense in this situation.
 
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All of the previous comments are good. Now, let me summarize some of my points of view.
1) The bog should really have "pea" gravel for proper filtration and be lined with good pond liner material. Swimming pools use sand!
2) The bog needs to be deep, not long and should equal about 10% of the pond's volume. Water is usually pumped into the bottom of the bog through say 3/4" PVC piping constructed in a "H" pattern, center fed from the pump with each leg having numerous 1/4" holes (drilled through both sides) spaced every 3 to 6 inches. The "H" distribution piping is covered by 4" corrugated PVC drain pipe cut horizontally in half, so each leg is covered. Next cover the corrugated piping with about 12 to 18" of the pea gravel. Cover this layer of pea gravel with 1" thick heavy filtration media. Then fill the rest of the bog up with the pea gravel. The bog should have a discharge chute that is below the top of the liner and discharges into your pond.
3) The reason for the filter media is to reduce the possibility of any bog plants roots from working their way down and clogging up the distribution piping.
4) For reference, my bog is 24" x 72" x 48" deep and filters both a 1,500 gal and a 1,000 gal pond with lots of fish.
5) Depending on how much filtration you need to do, which would be fairly minimal if your pond is lined (which I highly recommend) but could be substantial if not, you will need to periodically backwash the bog. To do this, I connect a separate pump to the supply pipe to the bog and suck the water out from the bottom, which adding water to the top with a garden hose. I do this until the water discharge become clear. In my situation, my pond has a lot of fish in it, so I usually backwash the bog ever 2-3 years.
6) Bogs are great for fish ponds as they develop good bacteria that digest the fish's waste and keep the pond water crystal clear all year long. But in your case, with no fish and just a swimming hole, you will need chlorination assuming you don't want to get sick from eventually polluted water, hence reason #1 to fully line your pond. Reason #2 is that an unlined chlorinated pond will quite possible leach into the water table which I dare say that the EPA won't appreciate.
7) In constructing your pond. your really need to support the top 2-3 feet of the perimeter, preferable with concrete architectural block (shaped like a 6 sided diamond) and readily available at Lowe's or HD. Failure to adequately support the upper perimeter will most likely result in gradual cave-ins. Also, tuck in the pond liner half way up this perimeter wall from the inside to the outside leaving the top several rows of block exposed. Grade the surround landscape to just about 1/2 below the top course of blocks. Use a skimmer on a side opposite of the bog's discharge chute to allow natural circulation through the pond.
8) Finally,depending on the elevation of the bog in relation to the pond, I highly recommend installing a check valve on the pipe feeding the bog to prevent dirty water from draining back into the pond if and when the pump is off line.

Hope this helps and good luck!
 
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Hey there Koi4JT! I appreciate your comments, the check valve was something I had not thought of and makes total sense, it is those little things that when forgotten can create a terrible mess. Thank you. I have a couple updates and a couple more questions which have arisen.

Following some other people's suggestions I began posting and communicating with people on mud pond forums and fishing lake forums. There are very few people who have tried and have been successful with keeping a earthenbottom pond clear. In fact, as Meyer Jordan pointed out to begin with, it is impossible without being prohibitively expensive. The one recommendation I received was to build my bog on top of a network of milk crates or something similar and install a bottom drain to flush it out, a process similar to what you have suggested. Apparently this was done on a much larger scale and worked to some degree. My thought process was maybe build a raised a portion, like a box or cage, on the deepest end of the bog with an opening on top where I could drop in a pump to remove the sludge as I flush it out from the other side. It wouldn't be too difficult to build, I have lots of scrap metal, but I am not sure if that even makes sense or is necessary. Other people have dug separate ponds, as big as my whole system, just to use as a massive bio/media filter. In my mind, the "bog" I am constructing would work in a similar, likely less effective, way.

Reading about the safety of swimming holes and microbial growth is a disenchanting exercise and I recommend it to absolutely nobody. I am fully aware of the risks of bodies of water and will do my best to provide a safe environment for myself and others but there is danger everywhere. I can only accomplish so much with the resources I have available and fail to see the logic in spending an inordinate amount of time and money on keeping a "natural" body of water sterile. As far as chlorinating the pond I do not think that is an option for me. Our family group that lives on the property absolutely prohibits the use of bleach, caustic chemicals, pesticides, etc. They are very, very, environmentally conscience. (For example, I live in a separate house and they get upset if I use bleach to wash my sidewalks because it "kills the plants and gets in the aquifer". You have to love old hippies but you cannot always reason with them.) I spoke with a fellow who may be able to help me procure a UV clarifier in the long term but I have no plan until then. In addition, to actually sterilize a pond this size with UV would cost 1000's. I have to do more research to see if a smaller UV sterilizer on a pond this size would do any good at all or just waste electricity. If that plan does not work than I will have to hope that aeration and the introduction of good bacteria will be enough to keep the body of water relatively safe.

I have been searching for cheaper alternatives to lining the pond and constructing a filtering system and have accumulated quite the hodge podge of things to use. I have some liner scraps from previous projects and some my neighbor was planning on using but doesn't have a use for now, 300 lbs of bentonite clay, a large stack of cinder blocks I forgot I had on a pallet in the woods, and a pile of leftover cypress boards from a deck we built. The plan is to drain the pond, pack down the clay, seal the edges where it may leak with the bentonite clay. Because the hole holds water would it be completely insane to use the liner I have to line the pond in overlapping portions solely to minimize the amount of debris that is kicked up? I believe I already have a good solid basin, I do not think I need the liner to hold the water in. The idea is to drape the liners over the sides, tuck them in or under the berm, and then lay a liner on the bottom. I could use the random cinder blocks to construct a ring around the base which would prevent the liner from floating up at all. I am open to criticism and fresh ideas. I cannot afford a full liner at the moment and waiting on funds would delay the project for an extended period.

I filled the pond to maximum capacity overnight (accidentally on purpose) and monitored the water as it drained out to find leaks and measure overall drop over the course of a hot week. For reference the pond has 2 foot tall "berms" circling the entire hole. I don't know if you can tell by looking at those pictures but the ground level is where the layer of dirt is when you look at the striation, the mounds above that is just the clay that I haven't been able to move around. The water filled and was overflowing the lowest edge of the mounds, it was pretty scary actually, I thought all those layers where you can see it already eroding away would erode further and cause the "berms" to cave in with it.

The water drained out under the berms, where the excavated clay just sits on the topsoil, but stayed steady after that for a week. So, the soil ring at the top is either super saturated or only allowing small seepage which works for me. The water settled out and was a nice clear green color until I entered the pond and would become that murky grey once again.

I dont have many days to work with and didnt want a giant stagnant water hole while I wait for my time off so I drained the pond yesterday. To nobody's surprise there has been significant erosion on the two walls visible in the picture above and a nice thick (foot deep if not more) layer of mud that is now sitting at the bottom of my project hole. To prevent more erosion I though about sinking cypress logs vertically at each corner of the hole and then laying cypress boards behind them to form a barrier. I could also just allow the erosion to continue until it forms a more natural slope and then lay the liner over that after I pack it down.

Please keep in mind I cannot keep this hole dry, there is a continual ground seep from two spots that feed this pond. In order to get the pond free of muck so I can line it I need to continually pump out the water and shovel out the mud. OR I am going to rent a diaphragm pump and let the machine do the heavy lifting when I have weekend off.

Lots of fun in the mud for me to come. Again, all criticism, skepticism, and input is appreciated! Thank you all for your help.
 
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Hey there Koi4JT! I appreciate your comments, the check valve was something I had not thought of and makes total sense, it is those little things that when forgotten can create a terrible mess. Thank you. I have a couple updates and a couple more questions which have arisen.

Following some other people's suggestions I began posting and communicating with people on mud pond forums and fishing lake forums. There are very few people who have tried and have been successful with keeping a earthenbottom pond clear. In fact, as Meyer Jordan pointed out to begin with, it is impossible without being prohibitively expensive. The one recommendation I received was to build my bog on top of a network of milk crates or something similar and install a bottom drain to flush it out, a process similar to what you have suggested. Apparently this was done on a much larger scale and worked to some degree. My thought process was maybe build a raised a portion, like a box or cage, on the deepest end of the bog with an opening on top where I could drop in a pump to remove the sludge as I flush it out from the other side. It wouldn't be too difficult to build, I have lots of scrap metal, but I am not sure if that even makes sense or is necessary. Other people have dug separate ponds, as big as my whole system, just to use as a massive bio/media filter. In my mind, the "bog" I am constructing would work in a similar, likely less effective, way.

Reading about the safety of swimming holes and microbial growth is a disenchanting exercise and I recommend it to absolutely nobody. I am fully aware of the risks of bodies of water and will do my best to provide a safe environment for myself and others but there is danger everywhere. I can only accomplish so much with the resources I have available and fail to see the logic in spending an inordinate amount of time and money on keeping a "natural" body of water sterile. As far as chlorinating the pond I do not think that is an option for me. Our family group that lives on the property absolutely prohibits the use of bleach, caustic chemicals, pesticides, etc. They are very, very, environmentally conscience. (For example, I live in a separate house and they get upset if I use bleach to wash my sidewalks because it "kills the plants and gets in the aquifer". You have to love old hippies but you cannot always reason with them.) I spoke with a fellow who may be able to help me procure a UV clarifier in the long term but I have no plan until then. In addition, to actually sterilize a pond this size with UV would cost 1000's. I have to do more research to see if a smaller UV sterilizer on a pond this size would do any good at all or just waste electricity. If that plan does not work than I will have to hope that aeration and the introduction of good bacteria will be enough to keep the body of water relatively safe.

I have been searching for cheaper alternatives to lining the pond and constructing a filtering system and have accumulated quite the hodge podge of things to use. I have some liner scraps from previous projects and some my neighbor was planning on using but doesn't have a use for now, 300 lbs of bentonite clay, a large stack of cinder blocks I forgot I had on a pallet in the woods, and a pile of leftover cypress boards from a deck we built. The plan is to drain the pond, pack down the clay, seal the edges where it may leak with the bentonite clay. Because the hole holds water would it be completely insane to use the liner I have to line the pond in overlapping portions solely to minimize the amount of debris that is kicked up? I believe I already have a good solid basin, I do not think I need the liner to hold the water in. The idea is to drape the liners over the sides, tuck them in or under the berm, and then lay a liner on the bottom. I could use the random cinder blocks to construct a ring around the base which would prevent the liner from floating up at all. I am open to criticism and fresh ideas. I cannot afford a full liner at the moment and waiting on funds would delay the project for an extended period.

I filled the pond to maximum capacity overnight (accidentally on purpose) and monitored the water as it drained out to find leaks and measure overall drop over the course of a hot week. For reference the pond has 2 foot tall "berms" circling the entire hole. I don't know if you can tell by looking at those pictures but the ground level is where the layer of dirt is when you look at the striation, the mounds above that is just the clay that I haven't been able to move around. The water filled and was overflowing the lowest edge of the mounds, it was pretty scary actually, I thought all those layers where you can see it already eroding away would erode further and cause the "berms" to cave in with it.

The water drained out under the berms, where the excavated clay just sits on the topsoil, but stayed steady after that for a week. So, the soil ring at the top is either super saturated or only allowing small seepage which works for me. The water settled out and was a nice clear green color until I entered the pond and would become that murky grey once again.

I dont have many days to work with and didnt want a giant stagnant water hole while I wait for my time off so I drained the pond yesterday. To nobody's surprise there has been significant erosion on the two walls visible in the picture above and a nice thick (foot deep if not more) layer of mud that is now sitting at the bottom of my project hole. To prevent more erosion I though about sinking cypress logs vertically at each corner of the hole and then laying cypress boards behind them to form a barrier. I could also just allow the erosion to continue until it forms a more natural slope and then lay the liner over that after I pack it down.

Please keep in mind I cannot keep this hole dry, there is a continual ground seep from two spots that feed this pond. In order to get the pond free of muck so I can line it I need to continually pump out the water and shovel out the mud. OR I am going to rent a diaphragm pump and let the machine do the heavy lifting when I have weekend off.

Lots of fun in the mud for me to come. Again, all criticism, skepticism, and input is appreciated! Thank you all for your help.

Hi Aschell90, OK I understand a bit more of were you are and where you want to go, so here are some more ideas and comments:

1) See if you can get hold of some decent roofing EPDM. It should be cheaper than pond liner which in your case doesn't matter because roofing EPDM can leach out plasticizers which are toxic to fish but won't affect you.
2) The bog as I referenced will become a "good" bacterial source that will or should keep the water reasonably clean being similar to lake water, but don't drink it.
3) Aeration will also help maintain decent water quality and if you utilize the flow through concept I previously mentioned (bog discharge to skimmer intake) your should eliminate any stagnation, which is the real problem causer.
4) I still recommend the CMU (concrete block) top perimeter border to stabilize the earth up to and beyond the pond. You should lay the liner as I previously mentioned but not necessarily do you need to totally line the pond. You could leave whatever FLAT bottom exposed. The liner is necessary to protect the excavated sides from erosion, which will totally mess up your hard work, but not necessarily so to retain the water. Nevertheless, a totally lined pond is the best. If you plan to use the bentonite clay, just fill the concrete blocks. If you use this stuff behind the blocks to fill the gap between the blocks an the earth, the bentonite will expand when wet and could possibly push you blocks into the ponds. I would recommend just reuse some of the better quality excavated dirt to fill in the blanks.
5) Very Important! You must establish a fence at least 48" tall all the way around your pond with a positive latching gate to eliminate the Attractive Nuisance you have created. It should protect you (legally) from wandering children, pets and wayward hippies, but not snakes or frogs.
6) And remember, you are trying to develop a miniature pond to cool your heels in, not a swimming pool per se. But keep in mind to build in a way to easily get out of the water via a ladder or something to make it easy to exit the pond.

Like someone somewhere said, nothing is ever easy!
 

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