Bog Gravel Filtration: Water Cleaned by Mother Nature

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

The headwaters of this stream function as the filter for this pond.

The headwaters of this stream function as the filter for this pond. (Click image to expand)

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.

Layout of Partition Bog Filter.

Layout of Partition Bog Filter.

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.

This raised gravel bog filter is ready for planting. (Click image to expand)

This raised gravel bog filter is ready for planting. (Click image to expand)

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.

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.

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.

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.

Can you spot the filter in this pond? It's all along the edges of the pond! (Click Image to Expand)

Can you spot the filter in this pond? It’s all along the edges of the pond! (Click Image to Expand)

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.

Small water gardens can be retrofitted with a pottery gravel bog. (Click Image to Expand)

Small water gardens can be retrofitted with a pottery gravel bog. (Click Image to Expand)

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.

Another example of a raised gravel bog filter. (Click Image to Expand)

Another example of a raised gravel bog filter.

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.

38 Responses to Bog Gravel Filtration: Water Cleaned by Mother Nature

  1. Justin McCarthy July 12, 2016 at 8:13 AM #

    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?

    • Lora Lee Gelles July 12, 2016 at 3:18 PM #

      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.

  2. Eric Dale Kimbrell August 7, 2016 at 10:25 AM #

    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?

    • Lora Lee Gelles August 8, 2016 at 2:14 PM #

      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.

  3. Preston August 23, 2016 at 12:01 AM #

    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.

    • Lora Lee Gelles September 28, 2016 at 5:59 AM #

      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.

  4. Dan August 25, 2016 at 9:56 AM #

    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.

    • Lora Lee Gelles September 28, 2016 at 5:55 AM #

      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

  5. Dan August 25, 2016 at 2:34 PM #

    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!

  6. Charlie Hind November 16, 2016 at 8:13 PM #

    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?

    • Lora Lee Gelles May 26, 2017 at 8:33 PM #

      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.

  7. Sherwood December 15, 2016 at 2:58 PM #

    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?

  8. Toni March 8, 2017 at 7:26 AM #

    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.

  9. William Irion March 19, 2017 at 9:22 AM #

    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

  10. Jim Morrissey March 30, 2017 at 1:24 PM #

    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.

  11. Katy Shanafelt March 30, 2017 at 7:28 PM #

    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

  12. Warren April 8, 2017 at 7:18 AM #

    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

  13. Mona Koltzau April 13, 2017 at 8:58 AM #

    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

  14. James murphy May 16, 2017 at 2:08 PM #

    The pond i have is big can i plant miscantus reeds in the bog gravel …?

  15. Philip June 5, 2017 at 1:08 PM #

    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).

  16. Lora Lee Gelles June 5, 2017 at 1:14 PM #

    Thanks for your input Philip!

  17. Jp June 23, 2017 at 11:28 PM #

    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?

  18. David Apple July 5, 2017 at 12:36 PM #

    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?

    • Lora Lee Gelles July 13, 2017 at 9:09 PM #

      From Author Anita Nelson:
      Yes this will definitely starve the bog.

  19. Allen O July 12, 2017 at 2:50 PM #

    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!

  20. Lora Lee Gelles July 13, 2017 at 9:12 PM #

    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.

    • Allen O July 21, 2017 at 1:35 PM #

      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.

      • Anita Nelson July 24, 2017 at 6:26 AM #

        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.

  21. Michael July 14, 2017 at 7:54 AM #

    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!

    • Lora Lee Gelles July 18, 2017 at 8:34 PM #

      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?
      ​W​hats 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.

  22. firman July 18, 2017 at 7:56 PM #

    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.

    • Anita Nelson July 24, 2017 at 6:23 AM #

      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.

  23. Sarah August 1, 2017 at 6:50 PM #

    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?

  24. Trudi Rankin August 12, 2017 at 2:28 AM #

    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

  25. Everton August 15, 2017 at 4:00 PM #

    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?

  26. Anita Nelson August 21, 2017 at 2:37 PM #

    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.

  27. Bobcat August 24, 2017 at 3:38 PM #

    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?

  28. Matt DiSilvester September 7, 2017 at 12:43 PM #

    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?

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