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.