Bogs are simple. Dig 12" down, lay a liner, fill with gravel, run water into it. Not sure what reusing the pump, skimmer, biofalls has to do with the bog...pond yes.

I like to fed the bog with the pump output, which sounds liek what you'll have, rather than putting the pump in the bog.
For this the bog water level has to be above the pond, liner overlaps making sure there's a gap between the 2 liners to stop wicking.

If you want the bog just for plants, which they're great, you can have any shape. If you want the bog to may be help clear water you want as long a bog as possible. Basically a below surface stream. You can wind a narrow bog back on itself so the result is any shape and the top can be covered in gravel so you don't see the bends. A narrow bog can also wrap around the pond several time, go out around the yard, anything you want.

THE source on this subject is Nelson Water Gardens. I recently built a mini-bog filter in a 15 gallon tote for a 100 gallon container pond. All my pond water is clear, but this is special. And the plants in the bog filter are growing like crazy.

I am finishing up the bog on my new 450 gallon pond. (I lack space, so little ponds get tucked in little spaces.) I have the plumbing almost finished, but I am fussing over it a lot more than with my barrel or trickle filters. Fixing a mistake is a lot harder when you have to move a few hundred pounds of gravel to get to it.

Rather than have the stream feed into the bog, I would suggest you build the bog away from the pond and let the bog water spill into the stream. This will look very natural, like your stream is spring-fed.

Here is a link that might be useful: Nelson Water Gardens -- bog construction

Thank you for your comments. I don't want to add another pump so I was looking for a way to tie what I have into a bog filter.

After a lot of reading I realized that I was overlooking an obvious and easy solution. Based on where I'm putting the bog area I can just use a valve to divert the water and run part to the waterfall and part to the bog. Duh! lol.

I don't have a lot of room to move the bog away from the pond, the 'stream' would of been just a few feet on each side at the max. This way though, it will be able to spill right into the side of the pond giving me places for oxygenated water to run into the pond.

Hi Angie, I'm doing something similar. The trick is "how to get the bog to upflow while at the same time using gravity to pull the water from your existing waterfall to the bottom of your bog".

So...place a very small pond inside your bog which will collect the water from the falls either directly or via the stream. (I got one from Craigslist) Make sure it reaches the bottom of your bog but will still also remain 1-3" above the level of water in your bog. This will keep it from just overflowing. Because your insert is inside your bog, a little splashing and a little overflow won't hurt anything

Fan out and away from your inserted pond several pieces of 4"-6" double walled black drainage pipe (Stronger and has smooth wall on inside; good for flow). At the farthest distance away from your pond insert, they should not be spaced out any further than 4' apart.

Now you know how many pipes you need to connect to your small pond insert. Place pipe next to pond insert, close to the bottom and mark to cut. Try to get a nice snug fit. We want the water to travel through the drainage pipes and be dispersed evenly throughout the bog bottom. If you have many pipes to attach you may want to pick up a coupler that looks like a peace sign. This will join 3 pipes into one fitting, which can then be attached.

Now that you have everything in place you will need to cap off the end of each pipe opposite the inserted pond. It may be unnecessary, but I am going to put a screen on the end that goes into the insert to keep leaves and other debri out.

You will also want the new pipes elevated about 1" for every 2' as they leave the insert towards the outer edges. This will allow you to use the very system you use to feed your bog to be reversed and backflushed. Just turn off your waterfall and stick a pump in your inserted pond.

With everything now in place take a skill saw and set blade to 2" depth. Cut slits every 18" apart for water to travel into bog. You may need to add more, but we don't want our water to escape into bog before it reaches the slits in outer edges. When done right, water should shoot out all slits without overflowing the new insert. How many slits are needed will depend on: how many tubes you used, waterfall flow rate, how tight your pipes fit into insert, etc.

Now you should be ready turn on your falls and see if you have enough slits. If you have water coming out abundantly, cut more slits, starting at the outer edges and working your way back to the insert pond . Do this until your water is coming out but not spraying out to forcefully

Does anybody know how the bog will overwinter? I am getting ready to replace my small pond with a much larger one, and incorporate a bog for filtering. I am in KY, and usually let the waterfall run all winter. It may freeze over, but the water runs freely under the ice. But a bog may be a different story.