We recently received a question on a previous blog: BOG FILTRATION, THE PERFECT COMPLEMENT TO BIOLOGICAL FILTERS. The question was:
Do you have any additional information about building and calculating an upflow bog with EcoBlox, like shown in the graphic at the end of this blog post? You already talked a bit about the surface area of the bog compared to the pond but what about the depth and the number of blocks stacked on each other for example?
I want to build a 15′ x 13′ pond with 3000 gallons and 9′ stream. Pond will be filled with stones and gravel, some plants and 20 goldfish (around 8″). How many blocks do I need and how do I arrange them for a fitting surface area of the filter? Do you have any recommended product to be used as tube under the blocks? Or do I have to build one myself? If so, do you have any instructions to do this?
Great question O Noble Ponderer!
Bogs are sized by surface area. 10% of the area of the pond in bog area is sufficient to consume all the nitrates a goldfish pond is likely to produce. At the other end of the scale are Koi, which need three times as much area, 30%, planted to bogs.
With 205 square feet of pond, 20 square feet of planted gravel will be sufficient. You have a 9’ stream, which simplifies matters greatly. What I would do is set one or two Eco-Blox at the top of the stream, on the existing grade on top of the stream liner. I would install two 2” or 3” flanges or bulkhead fittings on either side of the chamber thus created, down low so water enters and exits the Eco-Blox near the bottom of the block. On one side I’d attach the pipe from the pump, on the other a drain valve. Take a look at the sketch.
Water comes from the skimmer into the Eco-Blox on one side, flows up and out through a 4-6” layer of ¾-1” gravel on top planted to various low grasses or other aquatic plants, which are also planted in the gravel of the stream. The Eco-Blox under the gravel acts as a settling chamber. The outlet on the side opposite the inlet is valved. The valve is buried near the flange or bulkhead fitting, attached to a piece of pipe out to daylight somewhere.
I usually just set an 18” length of 4” pipe vertically over the valve so the handle can be accessed periodically to drain out the muck which will accumulate in the chamber. If I can’t reach the valve with my hand, I’ll slot the end of a pipe to create a wrench to turn the handle. This is necessary usually only once or twice a year.
You’ll have a great little active bog filter that uses the top of Eco-Blox chamber plus the stream to provide the necessary area for plantings. Plus a built-in settling chamber that will remove much of the suspended organic debris constantly and automatically. You may also consider adding a bottom drain to the skimmer, to pick up the rest of the debris. But that’s the subject of another post.
After reading so much on bog filtration I’m interested in incorporating a bog above my bio-falls water fall filter? In 2017 I built a 10x12x2 fish pond on my own. After learning a few mistake I made through trial and error, green string alga, rising bubble from hydrostatic pressure under the liner (from winter rain getting under the liner) and now a skimmer leak. I’m not giving up on my pond. I’ve now been doing more re-search on building ponds. It looked nice but was not functioning right.. So, Im now going to rebuild the pond and buy a new 40ml EPDM liner. And also making the pond 3 feet as well. I have a 5500 gph, submersible pump, Savio large skimmer and large waterfall filter. My bio-fall is on a small slope as well. Thought maybe If it’s possible to incorporate the bog filter on top of the falls somehow? And also, would I just use my pump for the waterfall and bog filter? Thought could I take the top lid off the waterfall filter and build a raised bog. Somehow drilling 2 holes in the top of the waterfall filter and connecting to PVC tubing (with holes) filtering the bog.. I would like your feed back and maybe some easy to follow instructions on how to go about it, if all possible? Appreciate any idea’s?
Well Nancy, my first suggestion is to be sure to use a 45mil EPDM liner, not 40 mil, for its greater puncture resistance. It doesn’t make sense to skimp on such an important component of your water feature.
You can go ahead and make a dedicated Eco-Blox bog like the one pictured. Simply split the flow from your pump to feed a bog AND your biofilter. Use a 3″ ‘T’ or ‘Y’ as close to the skimmer as possible to act as a non-restrictive manifold. Install 3×2 reducing bushings in the T or Y so you can use 2” Sch40 flex pipe all around. Feed the line from the skimmer into the stem of the T or Y, then run one 2″ line to a planted Eco-Blox upflow bog at the head of the stream. See the sketch posted with the blog. Run the other 2″ line up to the biofilter, also feeding into the stream. You will probably increase the amount of flow with the two returns just because the double 2″ lines will let more water through with less friction than a single 2″ line. That being the case, you may want to make the stream deeper and wider than previously, with room for 3-5 inches of gravel on the bottom, and plant it heavily. As the water passes over the gravel, the plants in the stream will also remove some of the unwanted nitrates that would otherwise feed algae.
I would also strongly encourage you to follow Savio instructions and remove any filtration from that particular skimmer when using a pump that size. That helps keep pumps from burning out prematurely, a common issue when loaded filter media slows the water flow through the restrictive passages connecting the inlet to the small pump chamber.
Good luck Nancy!
Hello Demi, thank you for your suggestion and answering back so quickly. Yes, Im certainly going to use 45ml epdm rubber liner. ( That was a typo). I think I got the concept. All though my existing pond had a high 3′ waterfall w/no stream.. Reading your instructions I will incorporate a stream leading into the pond. Would I still install a deep and wide stream bed with 3-5 inches of gravel in the stream or on top of the Eco-blox?( A little confused) My pump is plumbed with a 2″ Sch40 flex pipe. So would I install a “T” at the pump with the same 2″ flex pipe but one leading up to the bio-falls filter and the other leading (connecting) to the eco-box Once the 2″ flex pipe is connected to the inlet of the eco-box does water fill the box and passes through the rock,gravel and aquatic plants and then down into the stream? Does the Waterfall filter come out somewhere else into the stream? I get the drawing and the concept but no sure about the waterfall filter? I would still have spring flo media and filter-mat in the waterfall filter but no filter-mat in the skimmer. Correct? Thought if you can be so kind is to draw another picture with the waterfall and bio-bog. Thanks for giving me such great advise. Can’t wait to get the pond rebuilt. But this time with a better out come. You really made some good points.
Hi Nancy, please check out our new blog: https://www.atlanticwatergardens.com/blog/2019/06/18/bog-filtration-questions-answered/ for the answer to your question. Thanks!
Hi! Is it okay if I have a separate biofalls and upflow bog filter? My biofalls will have a 5000gph pump and my bog will have a 2000gph pump both in the same skimmer box (different tubes both going around to the other side of the pond). My bog will be raised with a spillway fountain effect. My biofalls will be a typical stream and waterfall. The bog is 25% of the pond surface. Will this keep it clean? I want 3 koi maximum.
Hi! That’s exactly how I build my ponds – the biofilter takes care of the ammonia reducing bacteria and the upload filter takes care of all the sediment and the nitrates. 25% is fine because you have the biofilter – we would recommend 30% if you didn’t. Great technique! And it will handle the next 3 koi you’re going to have eventually, even if you don’t want them. 🙂
Dear Demi, in my case i would prefer to combine rainwater harvesting and the bog into a single design. My pond is made of brick and block with a rubber painted surface inside. The issue is that it is above the future rainwater collection area. Why does it have to be upflow, why not downflow? just reverse the system, maybe even add a filter membrane to collect silt etc for future bog plants. use the ecoblox and a deep pipe that would return the water to the sump. My aquarium filter works in this way. Filter media, bio material and then return to the aquarium. I estimate that my roof will provide 62,000 gallons of water to the area most of which will runoff as it is now.
Hello Demi,
I have an 1800 gallon koi pond with a small waterfall as the inlet and a stream outlet which flows into one end of a lower elongated 600 gallon ‘natural’ pond reserved for tadpoles and various other aquatic creatures. Water is returned to the uphill pond via a pump at the other end through a 1” underground pipe back to the waterfall. The large pond is quite clear since all ‘gunk’ flows down the stream into the natural pond. About every 3 years I need to clean out the lower pond; a dirty, smelly job.
I am thinking about making a bog filter where the water flowing out of the upper pond and into the stream would enter the natural pond at surface level then drain through 8” of pea gravel into 3” perforated drain pipes below and ultimately back to the pump at the other end.
Do you think this is feasible? John
Hi John. Yes, that would intercept whatever solids are suspended in the upper pond water, trapping them in the 8″ of pea gravel before they reached the lower pond, and the gravel bed would likely be easier to clean than the lower pond, especially if you set it up so you can divert the flow of dirty water away from the lower pond when you clean the gravel bed. But that begs the question – how do the heavier solids get down into the lower pond now? Usually food and koi wastes would be trapped in the bottom of the upper pond, unable to escape down the stream. I’m thinking maybe the koi are actually stirring up the wastes, lifting them into the water column, allowing them to overflow into the bottom – is that possible? We usually put the bog at the top of the upper stream, to intercept what is being pumped from the lower, but you’re getting good results the way it’s set up, so go for it!