Converting basin to active bog filter?

[Linda W]

I’d like to convert the basin that catches roof water into an active bog filter, but would love any advice you have before I cut PVC or shovel gravel. The basin is 5’3” x 2’5”, with water running to a waterfall at 9” in depth and room to heap up pea gravel to 12”.

The basin is the first stop after water goes through a 2,000 GPH pump below. (See thumbnail photos 1 and 2).

The water has gone from opaque green to pretty clear (thumbnail 3) after I added plants and frogs added tadpoles. Thank you, plant advocates on this forum! I’m not planning to have fish.

Questions:
1) Should I just add more plants and skip the hassle of changing the basin to a bog? I could add gravel and take the pickerel plants out of their pots. The lizard tail is already free- range. My contractor was worried about the roots going down the pipe to the pump, but another pond expert said that wouldn’t be an issue.
2) If I do put in a bog, would two 5’ x 2” pipes in a U configuration with a clean-out pipes at the ends be enough for this relatively small bog? I’d use just one, but as thumbnail 2 shows, the inlet is in a basin corner.
3) Which position for the slits? I’ve seen plans with up to avoid wearing out the lining and down to avoid dead zones in the gravel. Would to the side be the best compromise?
4) Which spacing for the slits? I’ve seen designs with them 1” apart or 4” apart. My engineer husband suggested that maybe they should be further apart near the pump, where the water pressure is highest. I don’t want to strain the pump.

Thanks for any advice you have. This friendly and helpful forum really adds to my sense of comfort and enjoyment in this adventure!

 

[combatwombat]

1) Should I just add more plants and skip the hassle of changing the basin to a bog?

You could do that, but probably won't work as well as active bog.

If I do put in a bog, would two 5’ x 2” pipes in a U configuration with a clean-out pipes at the ends be enough for this relatively small bog?

Yeah, that should be fine. How deep is the basin? I'd be more concerned with the gravel clogging/channeling than the pipes themselves. I'd personally design a way to backflush it.

3) Which position for the slits? I’ve seen plans with up to avoid wearing out the lining and down to avoid dead zones in the gravel. Would to the side be the best compromise?

I can't imagine water flow out of these slits doing any damage to an epdm or rpe liner, but what most around here do is point them down and lay some extra liner or underlayment beneath the pipes to protect the liner.

4) Which spacing for the slits? I’ve seen designs with them 1” apart or 4” apart. My engineer husband suggested that maybe they should be further apart near the pump, where the water pressure is highest. I don’t want to strain the pump.

It won't "strain" the pump as the friction is on the output of the pump—not the suction where it could cause issues—but it may reduce overall flow.

I think adjusting the distance between slits as you travel down the pipe is a good idea to even out flow. I believe @Rashad (and perhaps others) have done that. Calculating exactly how to space them is probably an amount of work beyond what it's worth.

 

[addy1]

My bog is big, My pipe slits were further away nearer the pump. All of my slits face down, an extra Piece of liner between the pipes and the liner.

The pea gravel helps remove fine particles and filter the water. But a area full of plants does a good job also in removing nutrients which = green water and excess algae.

 

[Linda W]

Thank you, @combatwombat! The basin is about 15” deep, but the water depth is 9”.

 

[Linda W]

Thank you, @addy1! You are an inspiration!

 

[poconojoe]

I say go for the bog.

I guess I'm weird for facing the slits up. My thinking was if any muck does happen to build up, the slits won't get blocked.

I made the slits in my 2 inch PVC pipes 1-1/2 inches apart and cut 2/3 through their diameter. I have two pipes, each 10 feet long.
I wouldn't worry too much about spreading the slits in various increments or distances from the pump or even any type of elbows being restrictive. I was worried about using standard elbows as verses wide sweeps, but no need to worry. When I open my clean-out stacks, the amount of power or pressure is tremendous.

 

[poconojoe]

Another thing I was worried about was that the water would only rise up through the gravel right above the pipes. But while it's running, I can see the water percolating on top of the gravel all over the place, even where there's no pipe directly below.
It's quite amazing how this can be. I don't know how it does it, but the water is somehow rising up through the gravel evenly throughout the bog. Cool stuff.

 

[Linda W]

Thanks, @poconojoe! I was worried about the wide sweeps and keeping it clean, but now I won’t.

 

[poconojoe]

Thanks, @poconojoe! I was worried about the wide sweeps and keeping it clean, but now I won’t.

Every 3-4 weeks I'll notice the water from the bog to the pond has slowed down a bit.
I turn off the pump, open one of my clean-out stacks, turn the pump back on and watch the water shoot out black for about 3 seconds, then it runs clear. I shut the pump, close the clean-out, open my second clean-out and repeat.
I jamb a piece of spare hose in them to direct the gunky water to a small garden. Good fertilizer!

After the clean-out the flow returns to normal and the water level in the bog raises an inch or two. Funny thing that makes perfect sense, the the extra water in the bog comes from the pond (of course), so the water level in the pond decreases a tiny bit.

 

[brokensword]

I say go for the bog.

I guess I'm weird for facing the slits up. My thinking was if any muck does happen to build up, the slits won't get blocked.

I made the slits in my 2 inch PVC pipes 1-1/2 inches apart and cut 2/3 through their diameter. I have two pipes, each 10 feet long.
I wouldn't worry too much about spreading the slits in various increments or distances from the pump or even any type of elbows being restrictive. I was worried about using standard elbows as verses wide sweeps, but no need to worry. When I open my clean-out stacks, the amount of power or pressure is tremendous.

@poconojoe ; you're not alone as mine are facing up as well. I got my directions from The Pond Professional on one of his web pages. IMO, the water will flow easier if facing up as there'll be backpressure if facing down (the bog bottom) though water will still exit laterally. I've dug up my bog v1 and didn't have any issues with pea gravel IN the tube but my tube is 4" corrugated drain pipe/tile, so lots of room.

 

[brokensword]

maybe I missed it, but where is your pump? Is the catch basin the first stop from the roof or is the pump pushing water into it? I ask because if water is being gravity fed to the basin, you're dependent on intermittent fills. So, I suspect you're also pushing water from the pond into the basin, yes?

Upon re-reading and looking at your pics, I'm not sure you have a pond per se. The idea here is that water has to be pushed to the bottom of whatever you turn into a bog. You need a water source for that, something that won't dry up or go low and starve the pump. The whole idea of a bog is that the pea gravel is a LOT MORE surface area for denitrifying bacteria to colonize. That's a huge benefit of bogs. The plants take up the resultant nitrates. Were it mine, I'd definitely do as much bog filtration as I could. Plants will help with clearing the free floating algae but the bog won't help with that. Bog filtration is for keeping the ammonia and nitrites from becoming a problem for the inhabitants of your pond.

 

[addy1]

I have no clean out, slits down, about 1/2 if not more through the pipe, zero issues in 10 years. But mine is big and deep and full of plants. It never slows down in flow.

 

[Linda W]

maybe I missed it, but where is your pump? Is the catch basin the first stop from the roof or is the pump pushing water into it? I ask because if water is being gravity fed to the basin, you're dependent on intermittent fills. So, I suspect you're also pushing water from the pond into the basin, yes?

Yes, there are two ponds below the basin and a pump pushes water up from the lower one. The picture that shows the empty basin also shows the white pipe where the water comes up from the pump. The water also comes down from the roof when it rains. There are about 2,200 gallons in the whole system and a 2,000 gph pump.

 

[Linda W]

Update: I did convert the basin to a biological filter, complete with pot-free plants. It has some pea gravel but mostly fist-size or larger rocks. The plants are in the soil from their containers. The water got murky for about two weeks, but now is crystal clear. Yesterday for the first time I saw a big frog swimming underwater. Thanks for all the good advice! This forum is so helpful.

 

[Lisak1]

Very pretty pond! And thanks for the update. Usually we get the initial question and then never hear "the rest of the story".