I have always been intrigued by the idea of turning waste into a resource, and that is exactly what a bog gravel filter does for you. It turns fish and plant waste into fertilizer (plant food). This plant food is then consumed by the plants growing in the filter. The happy byproducts of this process are clear water and low maintenance. If a bog gravel filter had a mission statement, this is what it would be:
To create an environment that maximizes organic decomposition and nutrient absorption, starving the (always-present) algae in the pond and keeping the water looking gorgeous!
Happy Customers
Here at Nelson Water Gardens we are so sold on bog gravel filtration that we will not build a pond without one, and for one solid reason: there are virtually NO callbacks from unhappy clients. They don’t call back because, with fewer pieces of equipment needed, there is less chance for breakdown; secondly, a properly constructed bog gravel filter only requires seasonal maintenance. That means more enjoyment of the water garden and less work for your client.
The only drawback to a bog gravel filter is that there is no fancy filtration system (or, as Cla Allgood of Allgood Outdoors calls them, “The Big Uglies”) to sell to a client. The bog gravel filter is designed and constructed onsite. If a client insists on a “big ugly” filtration system, we install one in addition to the gravel bog filter. In my opinion the loss of monies from not selling a fancy filtration system are more than made up by the peace of mind provided by no callbacks and customers who will be thrilled not just after the pond is constructed, but in the years to come.
Green Water
Let’s be clear (pun intended) about why ponds turn green. The green water is comprised of billions of tiny, one-celled, plant-like organisms called algae. Like plants, algae needs sunlight, carbon dioxide, water and nutrients to grow. Eliminate any one of these elements and it will not grow. Bog filters are extremely efficient at removing nutrients from the pond water.
This mission is accomplished by pumping pond water evenly through a gravel bed via a grid of perforated PVC pipework. The gravel provides the surface area for nitrifying bacteria to colonize. The bacteria reduce fish and plant waste into plant food. Growing in the gravel are bog plants that take up the plant food. The water is returned to the pond stripped of all nutrients, thereby “starving” the algae, which cannot grow.
Bog gravel filtration is not new. Mother Nature has been using this technique for eons, and in that context we call it an aquifer, swamp or marsh. NASA has experimented with the technique for waste treatment on space stations. Some Sanitation Facilities use it in wastewater treatment. In the pond industry, Dick Schuck presented this idea back in the early 1990s. Years ago I met a fish farmer who used this technique and ended up making more money from the plants he grew in the filter than the fish! Nelson Water Gardens has been building bog gravel filters for the past 18 years.
Learning From Our Mistakes
Eleanor Roosevelt once coined a saying that informs what we do:
“Learn from the mistakes of others. You can’t live long enough to make them all yourself.”
Over the last 18 years of constructing bog gravel filters, we’ve made plenty of mistakes and have also refined the process. We’ve given countless lectures and workshops and have learned from the feedback from the audience. In a backward kind of way, I’m going to start with the mistakes we made in order to remove immediately any preconceived notions about the technique.
In some instances the right way to do it seems wrong. For example, removing the soil from plants before planting in the gravel substrate seems logical, but don’t do it! And if a little bit of gravel does the job, then a lot of gravel should be even better, right? Well…not when it comes to depth of the filter bed. Build deeper than 12 inches and the system can fail. Surface area is key; the greater the surface area, the more filtration! So here are the top 10 mistakes made constructing bog gravel filters:Too deep a bed of gravel. This is the most common mistake made. You need no more than 12 inches of inch gravel substrate. If you are adding a gravel bog to an existing deep pond area, construct a false bottom.
The bog is too small. For water gardens, 10 to 15 percent of the surface area should be bog, and for koi ponds there should be 25 to 30 percent.
Wrong size gravel. Use 3/8-inch pea gravel. Period. End of story.
Not capping the pipes. Water follows the path of least resistance and will simply shoot out the ends instead of through the slots.
Not enough plants. Initially you should plant one plant per square foot.
Wrong plants. There are many aggressive species which can clog the pipes and grow out of the filter.
Washing the soil off the roots of the plants before planting in the gravel. Don’t do this! There is not enough nutrition in a new bog to sustain new transplants. Just knock the pot off the plant and plant it—soil, roots and all—directly into the gravel. We promise the soil will not “contaminate” the bog or pond.
Not taking the plants out of their pots. This severely limits the plants’ ability to absorb nutrients and defeats the purpose of the bog gravel filter.
Starving the bog. This happens when a pre-filter* is placed on the intake of the pump. This not only stresses the pump but defeats the entire purpose of the bog by starving the plants of the nutrients that are being caught in the pre-filter.
*We are speaking of a true mechanical pre-filter (usually made from foam pads which need frequent cleanings) and not a pump protector or intake screen.
Not installing a clean-out pipe (or pipes).
Even Wrong Can Be Right
Even a bog gravel filter constructed all wrong works to a certain degree. Near our shop, our local county park installed a koi pond. Unfortunately, it was built without any filtration, and you couldn’t even see an inch into the water. Eventually the pond was retrofitted with their notion of a bog gravel filter using 3- to 5-inch rock instead of -inch gravel. (Why? I don’t know!) Additionally, the plants were left in their pots in the rock substrate. Despite these drawbacks, the pond did clear to a 12-inch depth! It has since been redone properly.
>> Related Content: Plant Options with Bog Filters
Building a Bog Gravel Filter
A bog gravel filter can be constructed in any number of ways. Examples of the most common configurations we have used in constructing water gardens include:
Partition: The filter is within the pond, separated by a porous retaining wall.
Raised: The filter is built next to and higher than the pond; water flows back via a stream or waterfall.
Border: A ledge, 12 inches deep and as wide as it needs to be, is constructed around the perimeter of the pond. At the edge of the ledge a porous wall is built to retain the gravel.
Island: Created by building a porous retaining wall on all sides in the middle of the pond.
Pottery Bog: You can create a filter from decorative pottery! Pottery bog filters are great for small ponds or additional filtration for larger ponds!
Directions for Creating a Partition Bog Gravel Filter
Follow the usual directions for building a liner pond. Size is determined by pond surface: 10 to 30 percent of the pond surface should make up the bog. If you plan to stock a lot of fish or koi, go with a larger size. Remember that you don’t have to dig deeper than 12 inches in the bog area. Ideally the entire area, pond and bog, should be constructed with one sheet of liner.
Using cinder block, stone, bricks or any other stable building material, construct a dry wall (no mortar used) to section off the bog filter from the rest of the pond. One technique we recommend is using cinder blocks (painted black with exterior latex paint) and then “capping off” the blocks with a decorative stone of your choice.
Figures 1 & 2 illustrate burying the pipe from the pump to the filter. However, where possible, we recommend laying a flexible tubing* in the bottom of the pond. Just run the tubing through the lower portion of the wall connecting the pump to the distribution pipes in the bog filter. Put a PVC female adapter fitted with the appropriately sized hose barb fitting to receive the flex hose from your pump.
Install the pump on the opposite side of the pond from where the bog filter is located. This is to facilitate good circulation of water throughout the pond. Select a pump that will turn the volume of the pond over every one to four hours. (You can go with a higher flow rate if you wish.)
Piping Directions
In all but the smallest of bogs use 1.5” to 2” PVC pipe. The larger diameter pipe allows for better water distribution and easy maintenance of the piping over time. The outlet of the pump also factors in when determining the size of the pipes. Always bump up the pipes for efficient use of the pump. For example, use 2” pipe on pumps with 1.5” outlet.
The PVC pipe is cut with slots approximately 1 inch apart; the slots should be cut approximately 1/3 of the way through the pipe. (A Circular Saw or Grinder works great.)
Next, lay the distribution pipe on top of the pond liner in the area partitioned off for the bog filter. Be sure the slotted portion faces up. Gravel bogs 2 to 3 feet in width can be fed by a single line of pipe. Wider areas require additional lines, spaced 2 to 3 feet apart. This layout is similar to setting up a septic drain field.
The end of each line of pipe should have a “cleanout.”** Cut this pipe (now referred to as the “cleanout pipe”) to discreetly rise just above the gravel bed.
To accomplish this, use a sweep elbow or double 45-degree elbow to join the distribution pipe to the vertical cleanout pipe. The cleanout pipe is capped with a female adapter and a threaded cap. Spray paint the cap black or brown and it will “disappear” from view.
Once you are satisfied with your piping layout and location of the cleanout pipe(s), glue all parts together. Hook up to the pump and turn it on the see if the water is evenly distributed.
*Using tubing within the pond means less possible leakage, easier repairs, and less likelihood of damage.
**The under-gravel pipes can be cleaned out by simply removing the cap from the cleanout pipe; water pressure from the pump will help dislodge any debris that has collected in the pipes. You can thread a hose barb adapter to the female adapter and attach a piece of flexible tubing to recycle this nutrient-rich water into a flower bed! A reverse flow can be achieved by turning off the pump and putting a pressure washer down the stand pipe.
Planting
Now you are ready to shovel 3/8-inch pea gravel into the bog gravel filter area, but only fill halfway (the rest of the gravel will be added during the planting). Remember, stick with 3/8-inch pea gravel!
Most gravel is not very clean. Wash it as best you can before adding to the filter, but be aware it will muddy or cloud up the pond. Do not to worry; it will clear up. After all, that’s what the filter is designed to do! Now that the construction process is finished, it’s time to plant your bog.
Select your bog plants and arrange them in the bog area that has been filled halfway with gravel. Be sure you stay away from the plants in the middle list. It’s best to plant the tall plants towards the back of the filter, and lower growing plants in front. Create interest by contrasting plants with different foliage colors or textures.
Slip the plants out of their pots and place them with soil intact on top of the gravel. Do not wash the soil from the roots! There is not enough nutrition in a brand-new bog to sustain the plants. (Trust us, the soil will not wash into your pond.)
After the plants have been placed, gently shovel in the remaining gravel. Your goal is to place the plants at the appropriate level so that when the rest of the gravel is added, the gravel will be at or above the water level. In other words, no standing water in the gravel filter area.
Turn on your pump and your bog filter is now off and running with years of clear water enjoyment to come.
Does it matter what time of the year the bog filter is built and started?
What plants will live through the winter and be suitable for removing nutrients?
If started in winter when can fish be added to the pond?
Hi Justin.
Here’s your answer from the author, Anita Nelson:
Weather dependent, it doesn’t matter what time of year the filter is constructed. We live in zone 9 and our crew builds them year round. Demi on Long Island may have a different answer. Plants that live through the winter here are creeping jenny, sweetflags, Louisiana Iris, variegated celery. Also Lizards Tail but it can be invasive. Also you can grow lettuce in a bog filter during the winter months here along the Gulf Coast. Fish can be added any time weather dependent.
So as you can see winter is not an issue for us but it may be for the person asking the questions. All I can say is use common sense, if you can’t grow anything in the winter due to your climate then the same will hold true for a bog filter and adding fish.
So I built a gravel bog last year at the end of my pond. Planted it with horsetail rush at either end. Pickerel rush in the middle and corkscrew rush behind that. Also planted a small mound of Siberian iris at one corner. All was well. Everything wintered over well and then I noticed this spring it started backing up on the side opposite the iris, overflowing into the yard. So I removed the rather thick mass of horsetail rush from that side but that didn’t help. So I flushed the lines and that didn’t help. Then I built the side a little higher and added more gravel. Still nothing. So I thought maybe the iris mass was too thick so I removed them. Nothing. So what’s my problem. Why is it not draining back into the pond like last year?
From author Anita Nelson:
I think it’s due to the mass of roots in the bog which lifted up the gravel so that it is higher than the ledge of the pond. Horsetail can be very invasive in a bog situation.
I’m wondering how often I should have my gravel cleaned if at all. Also, when cleaning the gravel, is there any procedure to ensure the beneficial bacteria is preserved? Thanks!
I actually have several questions…
I’m new to the “bog filter” idea. Around my area, it doesn’t really get used. However, I love the idea of letting nature do what it has done for thousands of years!
Anyways on to my questions…
I have a small (500 gallon) pond in my front yard. During spring and summer, it only gets enough sun to maintain partial and full shade plants. What plants would I use in a bog for this area? Also is there somewhere you can recommend going online to learn about a pottery bog. Since I stated earlier, it’s a small pond.
And last, I’m currently constructing a large 5000 gallon above ground pond in the back yard. Here, it’s gets full sun almost all day. Maybe up to 3 hours at most of shade. I want to construct a bog filter here as well. What plants would work well here? I’ve heard that Iris and cat tail are good choices, but I know both can spread very fast and furiously. I’m in Zone 6b. So it does get pretty cold here in winter. And I’d prefer perennials if possible. Thank you.
From Anita:
First of all, nearly all bog plants tolerate partial shade, it makes sense if you think about it. The bog plants have to grow along pond edges where trees and other taller plants grow, so they have to adapt! I do know that Lizard’s Tail can grow in almost full shade!
I feel uncomfortable recommending plants for zone 6b, I’ve had no experience growing plants in those conditions. For example we would Never recommend growing cattails in a bog, yet my brother (who doesn’t listen) planted cattails in his bog to great success. He lives in Lubbock Texas which is Zone 6 I believe. The cattails did crowd out all the other plants though.
Can you let me know what sort of routine and annual maintenance would be required for your bog gravel filter? Also, what would I need to do to winterize the bog gravel filter?
Thank you in advance.
Here’s what we do as far as bog gardening maintenance. After a freeze we trim off all the free damaged foliage and then assess the gravel. If the gravel has lifted up (this happens as the plant roots fill in the gravel bed and the gravel will rise) then it’s time to thin the plants, and bring the gravel back to it’s former level. We recommend that all gravel bogs have a clean out pipe. A clean out pipe is really a stand pipe except it “stands” up out of the gravel and is capped. To clean out the pipework under the gravel in the bog, turn off the pump, remove the cap and then stick a powerwasher into the pipe to blow out debris and plant roots from the slots. If a powerwasher is unavailable then leave the pump on and uncap the cleanout pipe allowing the water to flush through, removing any loose debris and plant roots in the process.
I can’t wrap my brain around the gravity fed thing—that person is going to have to experiment on their own. As far as the stream goes, we’ve found the stream itself will act as a filter! – Anita
One more question. Is it possible to redesign the bog filter so that it is gravity fed from a bottom drain and then pump the water from the bog filter up a waterfall (my waterfall is going to be a few feet higher than my bog)? Or, could you make the bog filter more like a stream… the water enters one end of the stream, flows across the bog filter (as opposed to filtering up through the rocks) and exits the other end?
Thanks again!
How do you manage an above-ground bog filter in a planter in the winter time? Should all the water be drained out of it? Should the plants be removed and put deep in the pond?
From Mike White:
This depends on how cold the winter gets and the size of the above ground bog. If you are in an area that is colder then zone 6 you can get some pretty cold weather and the bog should probably be shutdown. This again will depend on the size of the bog and how protected it is. The question becomes if it were a pond that nothing were to keep a hole in the ice would it freeze solid. If the answer is yes then it probably should be drained for the winter.
I live in zone 5a borderline 4b: Wisconsin. I have not built our pond/bog because I know both will freeze solid.
If I make a raised bog and drain it for winter: will all the plants die?
If I incorporate the bog in the pond itself, will the pipes crack?
I put a small 50 gallon stock tank in the ground last year. Half planted bog, half open. No piping or pump. It froze solid and plants were fine. As an experiment it’s been okay but it is not the vision I was hoping to see.
I would like to use a bog filter with a rock bubbler type fountain. That would require having the output of the pump go to the fountain and so I need to reverse the flow through the bog filter and connect the pump’s intake to border type bog filter’s pipes. My purpose is to filter out bird droppings and reduce algae growth. Is there any reason a reversed flow would not work?
I have had my koi pond for about 4 yrs. I spend most of my weekends cleaning filters scooping ECT. This year I have decided to try the bog filter adding it to my exiciting pond. I enjoy my fish and my pond I have been doing a lot of research on the bog filter, must say it seems to good to be true. Although it makes since. Any advice would be helpful.
I have a 100 gallon stock tank I’m going to use for six goldfish and two red eared slider turtle’s and I’m using a 50 gallon stock tank for the filter I know in a turtle aquarium you need a pump to turn the water over three to four times an hour what type of pump should I use for this and is there one that is recommended
I have a 6000 gallon pond with skimmer box that pumps to a outlet box from the bottom of the outlet box. It flows into an 8′ basin and down a waterfall to pond. Can I install a bog filter when the water comes from above instead of below. Thanks for the help.
Hi Pond trade!
I am the newsletter editor for the Idaho Water Garden and Koi Society. I was hoping to use some of your information from your bog and koi pond article in my publication. Thank you for considering my request!
Thank you!!
Katy
I’m new to the bog garden idea. I live in Baltimore md zone 5i think I have been told to drop my bog plants off my shelf to bottom of pond if I build a 10foot square bod filter to n main pond it would not allow me to drop to bottom of pond an get it back on ledg in spring.wanted to plan my dwarf cat tails black game cock iris and picker rush in bog would they winter if I could only lower them Six inches for wint or should I not lower at all. Or do I need outer plants. Bog would only be about 8 inches deep would that work. All info I have found is just vague enough for failure .i have had pond twenty two years with clear water good water quality but still get hair alge on my lilies and water fall . Water fall is feed with up flow lava rock filter with two pumps and large pre filter water hyacinth in filter box helps but causes Oder flow issues as the fill in. Any help would be greatly .appreciated..I know I’m new to blogging but seem to be great source of experience advice
hi my name is mona koltzau, I’m an ex Californian from Carlsbad. we’ve moved to North Carolina. I found your web site and am so happy to see bog gardens featured, we are making a 3,300 gal pond and are going to put in a bog filter, that will be 4′ by 5′ 12″ deep but have had little success in getting details on the way to install the pvc pipes in the bog pond. we are new to making one. it’s going to be our first. Do you have any simple drawings that would help us to install in the right way? Ponds have been a part of each home we’ve lived in. I look forward to hearing from you. Any help would be very much appreciated.
Thank you, mona
The pond i have is big can i plant miscantus reeds in the bog gravel …?
Hi Pond Trade Team!
I wanted to send you a big “thank you” for these great instructions. I have just built such a natural pond gravel filter based on this web-page and it works like a charm. Within 2-3 weeks my little fish-pond in Romania went from very murky brown-green to quite clear, I can now see the bottom in 6-7ft depth!
I have uploaded some photos here: http://philips-florida-villa.com/pond-gravel-filter/
But I would like to suggest to add one important “mistake to avoid” to the list: if you build the filter-pond on a higher level than the main-pond, you have to make sure the water does not flow back down through the pipe once the pump stops – otherwise the filter-pond will be completely drained!
This can be achieved with a uni-directional-valve in the pipe or a pump with this feature. Or you can do it the way I solved it as a quick-fix: the pipe from the main-pond up to the filter-pond has to surpass (in altitude) the desired water level of the filter-pond at one point. But that’s not all, as I have found out the morning after smartly installing the high-elevation pipe: at the highest point you have to drill a small hole into the pipe (or even better install a small valve). Otherwise the filter-pond will still be drained by the siphon-effect (once the water flows backwards down into the main-pond, it sucks the entire filter-pond empty).
Hi Philip,
I see this is a old post but I just found it.
What type of solar pumps are you running.
Do you have a schematic of the setup pumps wiring etc…
Thanks Mike
Thanks for your input Philip!
I built the bog and it works well, but every time I top gravel off it raises the water level, I believe my exit may be too narrow. Any advice?
I am constructing a bio-pool with a full eco system filter and have been toying with adding a bog filter as last pass as the water enter back into the swimming area. A pump from under the bio filter will go to the bog filter. Do you think this will starve the bog filter, is this too much filtration?
From Author Anita Nelson:
Yes this will definitely starve the bog.
Hello! Thank you very much for providing this information. We had a Koi Pond installed several years ago by a professional who is associated with a major producer of pond products. I will not mention the name of the company because we have found that we are now pretty much on our own as they are not interested in returning to do maintenance due to travel time. They are helpful on the phone, but that only works to a certain extent.
Our fish have all gone over the falls into a “Dry Collection Basin” over time and we have not added any back in because of the constant battle we have with algae and green water. I say this because without the fish I am finding some success by “nuking” the pond with various chemicals. So far heavy doses of products containing Sodium Percarbonate Peroxyhydrate have worked the best, but I must use them several times per week and it is costing a fortune.
I just ordered an aeration kit and plan to install that as well as adding more plants as soon as I can get rid of the green water and hopefully stop the chemical treatments.
Although I never heard of it before, a Bog Filter is very appealing and I would really appreciate it if you could comment on the idea of putting it in a shallow area I have that drains into the “Dry Dollection Basin”… where all my fish have gone to die.
The details are as follows: We live in Central Florida. The Pond is 1,800 gallons. Of the 1,800 gallons, 600 are underground with the pump. There is Bio Filter at the top of the pond that flows into about a 5 foot stream. This stream spills into the main pond. At the other end of the main pond is a spillway that goes another 5 feet and a small waterfall spills into something we call a Reflecting Pool.
The Reflecting Pool, in turn, spills into the “Dry Collection Basin” and drops into the 600 gallon underground tank that holds the pump.
This Reflecting Pool is where I hope I can build the Bog Filter! It is an approximate rectangle measuring about 2 feet wide where the waterfall comes into it. It is about 4 feet wide at the other end. And it is about 7 feet long. It is 5 inches deep. For simplicity, you can think of it as a 7’ x 3’ x 5” basin with pebbles on the bottom.
There is a 1 inch pipe pumping water into the far end of the Reflecting Pool as the water spills out the side along the 7 foot length. This flow from the 1 inch pipe keeps the water from collecting at the far end.
So after all that, the question is… Can I build a Bog Filter in the Reflecting Pool? It would be fed by the one inch pipe and the water fall from the main pond. My main concern is the flow… The water coming in from the falls is much greater than the amount coming in from the 1 inch pipe at the other side and the 1 inch pipe is what I would like to use to feed the water into the PVC.
Thanks again (very much) for considering this rather lengthy and complex question!!! I hope this is not too much!
From author Anita Nelson:
I don’t know how to answer this question without seeing the pond. I suspect that they may be overfeeding the fish. I would stop feeding the fish for a least a week and then assess the situation.
Hello again, Lora… I am hoping that you will answer my reply to your July 13th message. Again, we have no fish. The basic question is will a bog filter work if I build it as described in my message of July 12th. If you have a way for me to send pictures, I will be happy to do so. Thank you.
Based on your description I cannot visualize your set=up. Can you send pictures to info@nelsonwatergardens.com? Disclaimer we will be on a trip for two weeks and it may take a while to answer your question.
Hello!
I recently built a 2,500 gallon above ground pond with a bog system above the pond to act as a water feature and filter. I believe my bog is approximately 300 gallons
.
I’ve got a dozen or so plant varieties and been experimenting on different plants that enjoy this type of system.
Everyone loves my bog. And it seems to work well.
I know the plants are doing their job. They grow fast, big, beautiful and thick! And my water is pretty clear.
So 2 questions, how long must the water stay in the bog to be returned clean? I’m using a pump that’s rated at 4500 gph. Because I’ve always cycled my pond water twice the total volume per hour. Or at least 1 1/2 times per hour. But everyone I talk to says it’s too fast. But I work on the principal that runnikng that fast will eventually catch everything.
2nd question. My water is still a bit green. Not clear. Is that normal? If I look from above, i can see my fish. I can see the bottom. But when I put camera in the water, it’s green and cannot see across the pond all the way?
Thank you for the imput!
From Anita Nelson:
Water flow is fine. But to answer the question here are some questions:
What substrate was used in the bog? I think there’s a good chance a larger gravel or rock was used.
How old is the bog? Has it had time to fully mature from microbe and rooting of plants standpoint?
Are there a good number of fibrous rooted plants among the plant selections in the bog?
Whats the fish population?
What is the square footage of the pond and of the bog? It’s been given in relative gallon sizes and not square footage. We recommend 10% surface in light fish loads lots of lilies and up to 30% with heavy fish loads.
I think putting pre filter either mechanical or biological will not starve or give effects for plants in bog filter, mechanical reduce the debris in bog media and give longer life to clogging situation, biological will be another added habitat of aerobic bacteria and give fresh nitrate to the plant. This is a combination with pea gravel in bog itself, the nitrate still going to the bog.
I’ve dealt with customers who have put a foam pre-filter on their pumps which traps just about everything. Every time the water is green. However, I think that a pre-filter with large openings should be fine. I’m guessing 1/8″ but just guessing, it’s worth investigation.
Yay, these look like great directions! I’m about to start building my pond with a bog filter.
Most important question #1: You say if the filter area is deeper than 12″, make a false bottom. How? I’ll be using a stock tank, 24″ deep. Is the false bottom just to hold the gravel up, so I can put the plumbing and water reservoir under it, or does it need to be a waterproof bottom so the entire shebang is all contained in the top 1 foot?
Less important question #2: I’m planning an 8′ round stock tank for the pond with a 6′ round tank above for the bog. No other filters; I only want to add a skimmer basket to catch the leaves on the surface. It will have some goldfish and some occasional people and dogs swimming in it. 8′ round to 6′ round way exceeds the recommended 10%-30% surface area ratio. Is my bog going to starve? Should I make a smaller filter?
Hello I recently built a small natural bog feature which spills into my fish pond, it does look good and worked for about 2 days then the input pipe backed up and the water just spilled out of it.
I dug out the gravel (correct size) and made slits over the holes thinking the output was slower than the input hence the backing up. This again worked for about 48hrs then its overflowing again.The gravel is not getting stuck in the slits nor is it more than 12″ deep any ideas?
Thank you
Hi I live in the beautiful, sunny, Caribbean island of Barbados; I’m enthused by articles I’ve read online — including yours — about bog filtration and am considering using that system. So my question is: are they any special considerations for building a bog filter in the tropics?
I’m soooo jealous, living large in the Caribbean! OK down to business, our business Nelson Water Gardens is in sub-tropical Houston, so we experience hot humid weather for 9 months! There are no special considerations for your area, in fact your bog will work 12 months and not go dormant as it would in more temperate areas of the world.
I inherited a pond with bog area, it has a pump channeling water from the skimmer to under it and is then layered with pea gravel, lava rock and finally river rock with plantings. However it is not separated from the main pond – i.e. water flows freely both ways so the liner is not separating them in any way. How do I fix that?
Will this method work to some extent in larger ponds, say a half acre? I was thinking about adding something like a bog filter to my pond say somewhere around the 40 foot square size?
I used planted chamber also to prevent my water to turn green since the plants absorb the nutrients in the water
Hello, we have a very large pond with indoor sand and gravel tank filtration. We are looking to upgrade filtration. What options are available ? ( Pond – 500,00 gallon with fish )
Where are you located? With a pond that large perhaps I can hook you up with a local expert in Active Bog Gravel Filtration.
We inherited a small pond when we bought our house and have struggled for the past 4 years with pumps and filters and green water. We are currently investigating the bio-filter option but is it possible to add a bog ton an existing pond.
Yes it is possible, usually this is done by building the bog filter adjacent to the pond that is 1′ or more higher than the pond. Water is pumped into the bog filter and returned to the pond via a waterfall. If the water garden is big enough you can even construct an Island Bog Filter. For smaller ponds we have actually used pottery to perform two functions; decorative and the pottery houses the gravel and acts as a filter.
I love the idea of a bog (natural) pond. I am thinking about making a pond for my ducks. Is there any way I can incorporate a bog filter system in my duck pond construction? And are there any books you could recommend on this subject?
I don’t see why you couldn’t do this, I don’t know of any books on the subject but you may find information that is applicable in literature on Swimming ponds. These are ponds constructed for humans using the natural bog concept. I’ve never built one because of the poisonous snakes that abound here along the Gulf Coast but other areas of the country and Europe have built them successfully. My only caution is the that most ducks and geese produce a lot of “manure” so I would build my bog accordingly.
Hi Anita! Great article! I have a 35000 gallon pond that I struggle with clarity. It remains dirty all summer long. I have large trees around it so it gets a lot of leaves in fall and I constantly clean them out which I installed retro bottom drains, mega strainer baskets and a drum filter that filters down to 70 micron.its a 16000 gph system. It dumps out of the drum filter into aerater biomedia tank and the biomedia has never seasoned with any growth. I still have a lot of sediment in the pond which I brush off the liner into the bottom drains. it’s never-ending. If I build a bog is the drum filter too much prefiltration? I don’t want to have to constantly clean a bog either and even the water out of the drum filter is not very clear.
I have a question. I recently added a pond and the bog has pea gravel but the bog is under not on top like the the picture where the water has a water fall. Will it still do the job or should it still be higher?
I’m not sure I understand how your bog was constructed. The bog can be at the same level as the pond but under I’m not sure. How is the water returning from the bog to the pond?
I have a lake of 600m2 plus bog filter area of 200m2, my question is if my bog filter gravel is 0,5mts deep will this cause the system to fail as I see a 12 inch depth is stated?
I have an earthen pond fed by a spring with low flow in summer and heavy in winter. Diameter is about 30 feet, depth about 4′ (including muck). Of course, algae problem is in summer. How about a series of grow bags around a portion of the perimeter set on a ledge 1′ deep? It seems these would be completely permeable (good/bad?). Also any biological suggestions for muck? The pond is not in a good location for excavation. Wonderful to be introduced to this concept and your website. Thanks!
Here’s what comes to mind, could the flow from the spring travel through a gravel bed? Are you thinking of splitting the flow and having it travel around through bog “trenches” surrounding the pond? I just don’t know if there is enough water pressure to make this work. As far as the muck buildup goes the gravel bog will not help reduce it. I’ve heard that adding aeration to the bottom of the pond and using the enzymatic bacterias will reduce muck over time.
I wasn’t considering using the inflow for the filtration for the same reasons you expressed. Plus I think the fertility is already in the pond which hosts many amphibian tadpoles and adults (tree frogs and salamanders). I will use a pump to recirculate the already in the pond water through the filtration apparatus. I’m just trying to decide what container I will use to house the pea gravel. I have the grow bags but I wasn’t sure if the “reverse percolation” would be impacted by the porosity of the bag which in my opinion would be much greater than the concrete blocks with the pond liner, resulting in less of the nutrient-rich water getting to the bog plants in the upper level. There really is no ledge so I will have to create this working around and in the water. and the bags would not be too impacted by irregularities on the ledge. Another option which I think would look interesting is to use a small. 6-8 ft, ready for the dump, aluminum or fiberglass boat to house the gravel.either in the pond or just above it.
I am so pleased to be able to have this dialog with you. Thanks.
I have retrofitted my pond years ago by simply building a cinder block wall to section off part of the pond. No liner needed, you can even do it by stacking natural rock. I agree that the material used for grow bags would eventually clog up and defeat the purpose. The top of the wall could be slightly underwater with the gravel bed sloping up so that it eventually emerges out of the water.
Good idea. Thanks.
Hello,
I currently have a pond 2500 gallons in my back yard. It is doing well fish, snail and plants. I would like to build a bog filter using a stock tank.
Have you any experience with this. I was going to build a filter system using pipe and mats that I can remove. I would like to do some aqua-farming, lettuce and spinach, may try Tomato.
Thank you,
Greg
There is no reason not to use a stock but a few things to think about:
1. How to get water to and from the stock tank
2. Most stock tanks are deeper than 12′ so you will need to build a false bottom—this is all to the good since it makes cleaning a bog that much easier.
3. No reason not to grow lettuce, we’ve done it here in Houston during the cooler months and it grew just beautifully.
4. Haven’t tried spinach or tomatoes. We have had customers successfully grow tomatoes in a bog filter.
Has anybody every converted a swimming pool into a pond, cleaned by a bog filter? I have a friend who lives near Napa and the earthquake a few years ago left the distal corner along the length of the pool about 18″ higher than the corner. It is now full of algae. I know bog filters work, I had a neighbor who had one and crystal clear water but her pond was only about 30″ deep.
I haven’t heard of anyone who has done this but why not?
I have dug and lined a pond and created a bog area that is 25 percent of the surface area of the pond. Because the pond is 8 feet deep I made the bog the same to keep volumes proportional. My pond will be fed from a well which in this area of shale tends to be acidic. My thinking was to fill the bog with small limestone gravel to help buffer the pH. Since you recommend pea gravel, can I create a false bottom in the bog area by using a fabric between the two types of stone and maybe put my pvc lines under the fabric to reduce clogging? I always thought I would have the slots downward to prevent clogging but the fabric would change that. My pond is about 60000 gallons so I will need to push a fair amount of water. Do you think I could put my pipes about 4 feet down with the fabric configuration? Why do the systems fail anyway? Too much root system? Eventual filling with detritus? Your help is much appreciated as I am getting close and excited. Thanks. Reed
We’re not sure why a deep gravel bed fails but we suspect it’s a combination of lack of oxygen and build up of detritus. I have not had any experience with using different types of substrate that can affect the pH. As far as the configuration of the pond goes, you will have to use a heavy grating and plastic screening, I’m not sure how the fabric would hold up over time. Water is very corrosive. I assume the grating will be supported by 6′ pillars?
I wanted to know a little more about the pumps required and their placement which should be safe for the fish.
And do you recommend a surface skimmer along with the bog filter?
Dear Dr. Yasser
We use low energy magnetic driven pumps manufactured by the Daner Corp. We’ve carried these pumps for over 20 years and they come with a 5 year warranty. We rarely have a problem with fish getting caught in these pumps because we use a pre-filter screen. As far as the skimmer goes–if there are no waterlilies in the pond and you have a lot of leaf drop from nearby trees then by all means use a skimmer. Tree leaves tend to be caught in the waterlily pads but a skimmer can still catch quite a few. Good luck with your project!
Great info for sure…..Two points if I may.
1. Gph going into the bog or wetland area not so much the size of piping used is whats crucial.
2. Secondly be sure your cleanout port is large enough to at least get a small pump in there because many of our bog or wetland areas are deeper than 12 inches.
Fabulous and informative article. And thank you for addressing so many questions! I will be building a pond and big next year. I had planned on both water Lillie’s and a scimmer, but I see your comment that they are incompatible. Why is that?
They are not necessarily incompatible. It’s just that a lot of leaves and debris floating on the pond surface can get caught in the waterlily pads and not flow into the skimmer. I guess it all depends on how much surface area is covered by lilies. If more than say.. 60% is covered by lily leaves then I wouldn’t install a skimmer. The decision is entirely up to you!
I live in Central Florida and have a 4 year old 20’x10’ approx. 4,000 gallon fish pond with 11 goldfish/two koi, frogs, mosquito fish and snails. In August, 2017 I installed a 4×6’ bog, 14” deep, with 12” of 5/8 pea rock, planted reeds, and other water loving plants. In 48 hours I had a crystal clear pond. As the weather cooled as in the past, the pond plants died off along with the water hyacinth. All went well until the first cold front came thru our area in January, 2019. The water turned brown with a great deal of suspended matter. Over the next several weeks I vacuumed the pond, emptied at least 25% of the existing water and renewed the water, and did this again in 2 days but the water is still brownish. I did the jar test but there is very little heavy sentiment settling to the bottom. I used some additional additives that is supposed to clear water with very little improvement. Where do I go from here.
I have a 15′ x 17′ pond, 2.5′ deep with a skimmer on one side and a raised waterfall on the opposite side. I want to put in a bog in the water fall area. since it’s an existing pond, one liner is out of question. do you recommend anything special to add on a bog? What size would you recomend . I have a ton of goldfish, they just keep reproducing! Also, should my pump be in the skimmer or in the pond?
You have several options, the easiest would be the wall off a portion of your existing pond to create the bog. Or you could build another pond at the top of the waterfall but that depends on space and pond building skills. Since you don’t have koi I would recommend at 25 sq ft bog garden which translates into 5’x5′ or 2′ x 12′ or whatever shape you like.
I don’t have much experience with skimmers but I believe you should keep the pump where it is easily accessible, so you can clean the intakes when necessary.
Hi, great information thank you, I have a small pond of around 500 gallons and plan to add some fish so I’m thinking of making a pottery bog filter, can you tell me how many hours per day would you normally run the pump ?
Run your pump 24/7 for two reason, continual flow of oxygenated water for the beneficial bacteria in the gravel substrate and secondly pumps last longer if they are not turned on and off. If your concern is energy consummation most small pumps are Magnetic driven and comsume very little energy.
Hi
I’m a fish person from the uk.
We have tropical, marine and a koi pond so I understand the cycle. We have a 1500L pond with baby koi that we brought at 1” and now they are over 12”. We’re building a new 4000l above ground pond and want to put a bog garden in a planter that is built over the main filters. The problem is the bog would only be 4” till the water overflows back into the pond. Will this work? We suffer from green hair algae every year and I want my boys to have a nice new home. Thank you in advance for any help an advice
As you know water usually obeys the laws of gravity except in the case of wicking so (I’m guessing here) if you have a clean break between where the water flows down the 4″ back into your koi pond you shouldn’t have a problem.
Great article! I am going to build a 2500 gallon formal pond and was thinking of doing an under gravel filter and %15 bog. What are your thoughts on this type of setup?
By under gravel filter, I assume you are talking about an Aquarium style filter where air is pumped to gravel on the bottom. I have no experience with these type filters although I’ve seen them in operation in Northern parts of the country.
Hi Anita
Thanks for the reply! No there will be a very slight drop back into the pond. My question was really aimed at the depth of the bog filter itself. I’ve read else where it should be no more than 12” deep but mine would be only 4”deep ie the depth of the gravel.
Once again thank your for your help!
I am contemplating a natural pond within a bricked rectangle 13×16 ft. It is now a fallow vegetable garden. Would like it to serve as a water reservoir, emergency water supply, with flora and fauna, visually appealing and fed from roof gutters on nearby metal roof. I understand that a settling tank would be necessary. After reading about how to set up the natural gravel filter am uncertain about the best way to proceed and seeking guidance on setup. Located in central florida and plan to excavate 5 ft depth in center with 2 ft wide ledges on each side about 8 to 10 inches deep which will serve as the filter. Am undecided whether or not to install center drain at deepest point for pump out purposes. Plan to use an EPDM one piece pond liner with underlayment. Would appreciate comments or suggestions.
We have a pond at our store constructed in the same manner as you described, it has a ledge all the way around and we have a line of perforated pipe running through the ledge under the gravel. The edges are constructed simply of stacked rock but you could use brick—no need to make it waterproof either. The pump should be located within the pond itself so it can pull the nutrient rich water into the bog. The bog then strips the pond water of nutrients and returns it to your water garden.
I’ve just got 3 ducks and want to build them a bigger pond, rather than the small, tip out and empty one most people seem to use. Does anyone know if a bog filter could cope with the amount of “poop” ducks produce please?
I know ducks produce massive amount of poop so I imagine an active bog filter would need to be at least 30% of the surface area of your duck pond. Anyone else out there reading this have experience with duck ponds and duck pond filtration. BYW Duck rock and are great for keeping insects out of the garden!
Hi. This is interesting. Is there any one in (south/central?) Missouri, who builds/installs these for people? If so, please EMAIL ME At:
AppyHorsey@windstream.net
Thanks.
I am in the process of constructing an upflow bog filter. I live in zone 5, Missouri. I am planning on following your suggestions. I have several questions. 1) what is the latest (2019) pro/con for upflow. 2)Only pea gravel or layered sizes (2-3inch size on bottom, 3/4 next then pea gravel on top)? 3) only 12 inches (keep in mind I’m in zone 5)? 4) how do I winterize to keep pipes from ice fractures? 5) I pull water from bottom drain and use skimmer basket as prefilter. Will this be adequate? I have other questions but answering these might answer them. Thanks
Great article with lots of info and knowledge!
I have a nature pond that is fed by underground water so the pond has no liner at bottom. Are these ideas also applicable to this situation? Some people suggested me to install a thick fabric at the bottom to block off the mud and put river rock on top to hold the fabric. Will this help to slow down the water plants grow out of control? With fabric and rock install in the pond, I can also install a bog filter. Do you think that will work to clean the water and bring some clarity in the water for this nature pond?
How much water do plants in a bog actually drink causing water levels to subside ??? …I have four bogs with Huge Elephant Ear plants and others even a tomato plant. Certainly they must be drawing large amounts of water to thrive in this 100 degree Texas heat??? – GMz
Yes, you are correct, Texas State University in San Marcos did a study on this. It was conducted by Dr. Paula Williamson and she discovered that dramatic amounts of water were taken up by Taros. The Taros were an introduced species in the local Comel River and were removed. Not sure about the Tomato plant, but at least it delivers a fruit for all the water removed!
Hello
I’m doing a large pond project for a friend, it’s expanding a 40×40 x 6 ft deep pond to a 60 x 60 x 12 ft deep pond. The rest of his land is akin to a beautiful national park with as many trees, shrubs and plants that our semi permafrost area allows. (Edmonton Alberta Canada area).
He would like the water clear enough for swimming without the plants for natural filtration.
Is it possible to construct just a bog type gravel bed filtration system in the pond that would provide clear water for swimming in?
The pond will hold roughly 170,000 gallons
There will be falls and streams into the pond as well
I appreciate any advise I can get
I’m sorry that’s not a question I can answer! Conditions are so different here in hot humid Texas. I’m guessing with your shorter season that gravel filtration might be sufficient but I really can’t answer the question.
Hi,
I have a bog filter that is constructed as follows…
Void of approx 6 inches which includes bottom drain for cleaning/flushing (approx once a week in summer)
Feed from pump into void (via UV clarifier)
12 inches pea shingle suspended above void.
3-4 inches water above gravel – combination of oxygenating plants and various broad leaved plants/parrots tail/water mint.
Water flows back into pond via water blade.
Constructed April 2019.
Worked very well over the summer – plants grew rapidly – water very clear.
Now approaching winter I have turned off the UV clarifier and have the pump on a timer to operate 6 hours per day 1200- 1800 to prevent the bog becoming stagnant (I would imagine this will happen once the water stops flowing for any extended amount of time).
Do you think I am doing the correct thing by putting pump on a timer or do you have better recommendations for my setup?
Pond volume approx 4000 gallons – located London UK
This is a great article and comment chain. I have always had a bog in multiple ponds I’ve built and I’m researching my next build so I’m looking for ideas or best practices. I recently built an above ground pond with a 12 inch depth bog. It worked too well as I had too many fish and cleaning it out became an issue, and it was disgusting. I recently picked up some soda crates. They are half the depth of a normal milk crate, put some screen inside, then filled with gravel and plants. This allowed me to lift the tray out, and spray it down getting the muck out. It also let me wet vac the basin where the trays sat. I most likely going to build the next one the same, just much larger.
Is is safe to plant edible vegetable plans. Tomato, peppers etc…. Is there any safety concerns? Seems like the pond water with fish waste would be great for the plants.
As far as I know there are no safety concerns!
Hello,
I really enjoyed this article. Thank you for posting it! I am in the process of building a pond that is 8×14 feet. My plan is to pump the water 15 feet away and then up a 3.5 foot hill. At the top there will be a water fall. The water will flow back into the pond via a 15 foot stream. Can I put the bog in the stream? In other words, if I fill most of the stream with pea gravel and suitable plants, will there be a filtering effect? I am not sure if the water flow rate will be too great. We are still in the building phase so we can modify our design. We are going to dig the stream about 10 inches deep and of varying widths.
Thanks for advice!
Yes the stream will have a filtering effect!
I have a bog attached to my koi pond built per your guild lines. Thanks! The bog is 16 ft x 2 ft . A waterfall into a 1500 gallon koi pond with an under gravel filtration system feeding the bog. I keep the pond and bog free of debris, however, on top of the bog gravel a layer of what appears to be sediment keeps appearing. Should I be concerned and somehow remove the sediment?
The sediment is unsightly but harmless. You can cover with an extra layer of gravel and then you won’t see it!
Hi there! I have a stream in my backyard (ranging from 2-4 feet wide) that leads into a large creek (not quite big enough to be called a river!). The stream flows from a few culverts that collect the run off from the road and neighborhood. So the stream is quite dirty! Unfortunately all of that run off ends up in the creek where many people swim. I would like to create some kind of natural filter to make the stream cleaner, which will benefit my whole community with and added bonus of having a beautiful, CLEAN stream in my backyard! Would a big gravel filtration system work in this case? Any suggestions would be greatly appreciated. I must add that I am located in Southern Ontario in Zone 5 – I figure that may affect what type of plants would survive our winters!
Hello,
I have created a raised pond which is 10’x16’ and 22” deep. It does have koi and a few goldfish. I would like to build a bog along one side which would be 3’x10’.
I have three questions:
1. Is that size bog sufficient?
2. If no, what would be appropriate?
3. I’m on my own in this project. Lava rock is lighter weight. Can I use that instead of pea gravel?
Thank you!
I am upgrading my pond and I’m intrigued by the bog filter idea. I also read about some people that had horrible sludge buildup in their gravel, which can be toxic if stirred up. Does the bog filter gravel need to ever be stirred or rinsed to remove sludge? I have a submersible pump that does about 2300 GPH and I want my new pond to be about 3000 to 3500 gallons. I plan to make the bog 30% of the surface area. Will that pump be sufficient, and do you have any plans or pictures to show how I can incorporate a waterfall with the bog, so I can just use one pump? What I’m imagining is the water could flow over the top wall of the bog, but I don’t know how that works if the wall is not mortared and is permeable, plus the pump hose has to go around the side of the wall. It seems that the water would not flow over the stop if it has other places to just seep through. Also, what product do you recommend to prevent clogging of the pump? I get so much algae growing on my pump inlet screen, that i have to take it out once per week to clean it.
thanks!
First things first. It’s news to me about toxic sludge. If that is the case my guess is that the nitrogen cycle is not functioning properly. The end product of organic breakdown is non-toxic but the steps to it are nitrite and ammonia both of which are toxic. The conversion from ammonia (toxic) to nitrite (toxic) to nitrate (non-toxic) happens rapidly in a properly constructed and functioning system.
For the pump we suggest you turn the water over once every 1-2 hours so your pump should be sufficient IF after you have done all your calculations on head loss and friction loss and the pump is delivering at least 1500-2000 gallons to the bog filter every 2 hours.
If you plan to have water flow over the wall of the bog filter to create a waterfall, then yes we do suggest you make the wall as watertight as possible for maximum flow.
We use a plastic screen product that we make into a box using cable ties (super low tech) to encase the pump and increase the surface area over which the water enters the pump. You could construct one yourself if you can find the material or call us at Nelson water Gardens and we could ship one to you. Our phone number is 281-391-4769.
Hello, very nice article and great comments/questions/answers section!
I am planning to build my own 10’*7′ pond (around 1000 gallons) and I am thinking of fitting it with a pump to feed a raised “bird bathing” shallow water tray, from which the water should fall by gravity into one end of a narrow bog filter (max 2 feet across, about 10′ long) where the water should flow and eventually go back into the main pond.
Do you think a bog filter where the water comes from above instead of from below would work?
In this way I would also avoid buying and laying down the piping on the bottom of the bog bed altogether.
Not sure why this isn’t shown in your article as a possible solution, makes me think there’s something I didn’t think about.
[This thing I didn’t think about] might be one of those mistakes made by others that I might avoid repeating myself… (like Eleanor Roosevelt said)
Thank you!
I have seen this done at Family Tree Nursery in Kansas City where the water flowed (quite strongly) from a waterfall into a bog and they didn’t use any piping in the gravel bog area and it seemed to work. However the water was falling from a 3′ height and it was quite a strong flow. So I’m guessing that your idea would would if the flow rate was strong enough to penetrate most of the gravel area.
Thank you for your answer Anita,
I won’t have a very strong flow, I was thinking of about 500 gph (even though I think in liters, lol) which would cycle my pond once every two hours. I will make sure it falls in a way so that it will flow through the gravel.
Maybe through a grate with a sort of small pond from which it will go through the gravel bed.
The thing is that the gravel bed will be higher than the water level, so I am hopeful that the water flow (strong or not) will eventually go through it anyway.
Thank you for the great article and for the passion you put into it.
Question: The bottom of our pond is irregular, about 21’s deep. We were unable to make a shelf. Our plan is to use 2 large containers for the bog. The containers are 20″s deep. We’re planning to put cinder blocks in the bottom of the containers and the pvc will be above the cinder blocks. This means the pvc will be about 11″s from the top of the containers and below them will be the cinder blocks to create the shelf. The shelf will have cracks and crevices around the cinder blocks, it won’t be completely solid. Will this be a problem?
We built an above ground gravel bog about 1 1/2 ft deep and 7 ft by 10 ft, lined it with black plastic and planted about a dozen Juncus Blue Arrow Grass. The water is backing up now after a couple years and it is green. Is there a way to clean it without having to take all the gravel out every time?
Thanks Sandie
Hi,
Thank you for the informative article. We’re converting our 15m2 swimming pool into a natural swimming pool and we have two 2.5m diameter water tanks for the bog. We were going to cut them to 35 inches deep so there would end up being approximately 31 inches of gravel. Is this too deep? Would 12 inches of gravel work for cleaning a 1m deep swimming pool as it does for a pond? Thanks