Bog filter conversion

[Steiner]

Hello Pond People
I have two ponds; one is 1,800 gallons with koi and one ‘is a 800 gallon ‘natural’ pond for tadpoles etc. The natural pond is 18 inches lower than the koi pond. My submersible pump brings water from the lower pond to the upper koi pond where the water recirculates by gravity and spills into a stream that flows back into the natural pond. All debris and gunk flows into the natural pond.
I am planning to turn the natural pond into a bog filter. My plans are to use 8 inches of pea gravel with three 3-inch drain pipes underneath to drain the water into a sump where the pump returns it to the big pond. I will use many water plants and include low areas in the gravel to create ponds for tadpoles and frog. Any tips, suggestions would be appreciated.

 

[j.w]

@Steiner
I don't have a bog but lots do on here and will be here to help you soon!

 

[Steiner]

View attachment 155283@Steiner
I don't have a bog but lots do on here and will be here to help you soon!

Thanks very much. Am I posted in the right forum or should/can I move it to the pond construction forum.

 

[j.w]

Maybe it should be in the pond construction forum. You can ask @addy1 to move it for you or maybe she will see my post here for her and do it.

 

[GBBUDD]

The firs rule of thumb in bogs is up flow the water through the bog.
The bog should be between 15 and 30 % of the surface area of the pond.
The bog when planted heavily can have roots that grow 24 inches deep or more . A MINUMUM of 12 inches of 3/8 " river rock is the norm

 

[Lisak1]

That was the first thing I caught too - your bog should flow into your pond... not vice versa. While a natural bog is flow through, a constructed wetland filter is 100% up flow.

Post some pictures of your ponds and maybe some good ideas will "flow"!

 

[fishlips]

You can use a under gravel filter in a pond. Aquariums have used a down flow under gravel filter since the 1960s I have 4 running right now. I am also using two 250 gallon holding tanks for a mass of koi fingerlings. Before I added the fish each would process 2 ppm ammonia per day only using a Walmart air pump.

Here is the flaw with down flow system. Cleaning the rocks has to be done. As debris get stuck in a thinner layer on top. With the better up flow layout and larger rocks on the bottom some debris settles out before getting pushed up in the rocks. Add in a simple value and it eazy to clean out.

The biggest factor I find is dwell time how long the water is in the rocks. To fast and the ammonia and such fly passed the bacteria and back in to the pond. Dwell time should be 5-10 minutes. With only 8" of gravel you have to have a grid of pipeing and well planed inlets to get a good even flow to get full use of the rock surface area. The 3" main should have 1" pipes added every 6-8" covering as much of the bottom as possible. Each 1" line should be capped and have slits cut getting larger or closer as it moves away from the 3" line.

 

[addy1]

Thanks very much. Am I posted in the right forum or should/can I move it to the pond construction forum.

I moved it for you.

 

[addy1]

And welcome to the forum!

 

[Lisak1]

An aquarium under gravel filter is so different from a bog. And you landed on the most troubling part of dumping water into a down flow bog - the clogging that will happen so fast you won't believe it. The water will take the path of least resistance and flow over and out of the bog if you give it the chance.

 

[GBBUDD]

The whole idea of the bog is to slow the water down give the bacteria plants and microbes as much time as possible. That being said reducing to a 1" pipe even though if enough lines are added it still keeps the pressure up in comparison to doing the same with a 2" line or larger. that's the same principle as aqua blocks reduce the flow's pressure and distribute evenly across the bottom of the bog.

 

[fishlips]

Fundamentally water flows into a settlement chamber then into the rocks and back to the pond. The big difference is where the settling happens. One is in the water above, The other is in the void space made by the aqua blocks. There is a huge difference in the percentage of surface area used under gravel filters use 100%

The pipes under the rock have to be size to the pump. To small and the pipes can not match the pumps needs. To big and the water velocity will be to slow dropping settlement in the pipe works.

Granted up flow bog is far superior and the downflow/under gravel is less the ideal. Having said that I can also see that renovating a wildlife pond into a proper bog is less the ideal. It could bring with it the hassle of shutting down the pond, reworking plumbing, new liner you name it. Not to look over the fact that the wildlife pond is 18" lower than the main pond and feed with a in flow stream.

 

[Laaf]

Steiner, do you have any space above your fish pond to build an upflow bog? Then it can waterfall into your existing fish pond back down the stream to the natural pond where you can keep your current pump and have it pull from natural pond into your bog, to complete the cycle.

 

[GBBUDD]

To big and the water velocity will be to slow dropping settlement in the pipe works.

YES !!! that's exactly what you want to let heavy debris settle in the pipe so it does not clog the rock. Then if needed you back flush the pipes.
Allowing the heavy debris to settle gives it and microbes and insects like worms etc time to break it up. It is then washed away as it breaks up into the water column . where the rocks, roots and bacteria break it down even further.

you should have your system where the largest anything that gets thrown down to the bog is nothing bigger then a piece of a stem or similar . you should never have so much being pushed down there that would ever clog a 1" pipe or more. The other key is to cut slits in the pipe about 1/3 of the way through the pipe. face up or face down has its own debate i can see the good in both. but ultimately use rocks that can not fall into your slits that should be at a minimum of 1/8 inch and I lean toward every 6 inches, with the baffle tubes every foot apart

 

[fishlips]

YES !!! that's exactly what you want to let heavy debris settle in the pipe so it does not clog the rock. Then if needed you back flush the pipes.

That was my mistake I was talking about pipes in a down flow system not how a normal bog works.