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My pond biofilter  RSS feed

 
pollinator
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Location: Zone 8b: SW Washington
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I just wanted to start a thread to illustrate the effect of a biological filter on my small pond.    This is sort of an experimental pond, in anticipation of building a much larger one.  I got it at Home Depot really cheap because it had a small hole in it, which I repaired.  I do absolutely nothing for/to this pond other than keep it topped off, and also circulate the water through a biological filter using a small pump.  I only do those things in the summer.   I have cleaned leaves out of the bottom twice in 12 years, and also removed a ton of duckweed after I placed a few plants in the pond then decided I did not like it after it covered the entire surface.

There are of course all kinds of creatures that live in and use the pond - mostly pacific chorus frogs, birds, and water boatmen, all of which just appeared.  The birds are attracted to the sound of running water, and also like to use the top of the biofilter for bathing.  I do occasionally have (I assume) raccoons in the pond which can wreak havoc with the pump in their search for food.  They have on occasion chewed on the tube coming from the pump and also on the power cord.

Due to the extremely rainy spring we've had, plus some pump repairs (the raccoons chewed up the foam intake filter) I am very late getting the pump in the pond.  I don't like to host mosquito larvae which is the main reason I put a pump in it in the spring & summer.   However I am certain that I have already hosted mosquito larvae this year - and there are tons of mosquitoes near the pond to prove it.  I do not want to put fish in the pond because I want the pond to be fairly natural, and also I don't want to worry about feeding the fish or worry about the fish becoming food for something else.  e.g. I see ponds around here with koi or goldfish, which get eaten by raccoons and herons, so people cover their pond with netting.  I don't want that hassle nor do I want to look at netting (although the pond is not visible from the house).

I just put the pump in the pond last night, and as you can see the water is full of suspended algae:


I have never paid close attention to how quickly the biofilter clears the water so I wanted to document it this year.  I will use this thread to do that.

Here are a few of the pacific chorus frog tadpoles:


There are tadpoles in the pond much of the year.

I'll post some pictures of the biofilter later.    Here is a rough diagram of the biofilter:



Water drops through the air where it picks up oxygen, then down a large PVC pipe .  It flows down the large pipe to the bottom of the biofilter, then it flows upward through a piece of "egg crate", i.e. plastic grid diffuser used for fluorescent tube lighting.  It continues upward through a large amount of lava rock, which provides tons of surface area for the microbes which do the actual filtering.  It then flows through a layer of filter fabric (like in your furnace air filter), although I have come to believe that this is not necessary.  Then, and this is the really important part, it flows through the roots of water plants which are sitting in pond pots on top of the filter fabric/lava rock.  The plans I followed (which are now lost somewhere in the ether) did not call for water plants, and I ran the filter for a month with only mediocre filtering results.  Then I was reading about microbes living on the surface of water plant roots, and thought I'd give it a try.  I put in three water grass plants from a local pond, and wow!  In a matter of days the water turned crystal clear.  So I am sure that 80% of the filtering happens in the plant roots.  This makes a lot of sense, because the main goal of a biofilter is to provide as much surface area as possible, and plant roots provide a lot of surface area. 
 
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What size is your biofilter?  From your drawings, it looks like you'll need more filtration.
 
Dave Miller
pollinator
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The biofilter is around 40 gallons, and is plenty big - I'll be posting pictures as it clears the water.
 
gardener
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Location: Central IL
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adunca wrote:
The biofilter is around 40 gallons, and is plenty big - I'll be posting pictures as it clears the water.



Very neat!  I can't wait to see the "pictures-in-action!"  Thanks for the cool drawing too.
 
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Location: Alaska
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I like it. A few quick notes though.

Firstly, fish are pretty fantastic. Assuming it doesn't freeze solid white cloud mountain minnows or sticklebacks would be good choices, reducing mosquito growth and typically having small spetites that can be met by other pond dwellers like daphnia.

Secondly, biofilter is something specific in the world of ponds and fishtanks, something that you have here to a great degree, but the plants aren't part of it. While plant roots have a fair deal of surface area a single clay pellet may actually have more surface area than a large plant, its counterintuitive but a reality. The main role of the plants seems to be nutrient export, where as a biofilter is primarily responsible for turning NH[sub]4[/sub][sup]+[/sup] into NO[sub]2[/sub][sup]-[/sup] and then NO[sub]3[/sub][sup]-[/sup]

Lastly what is your goal for the pond? If it is to look pretty then I'd say that you are set (because any pond looks pretty if it isn't covered in floating algae) but if you want to use it for something else then you may want to augment its populations a big. For instance Azolla production might be a good use for your pond, capturing Nitrogen from the air and then making a general fodder/green manure out of it, perfect for application to many plants.

Goodluck, I look forward to seeing what you do with the place.
 
Dave Miller
pollinator
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The weather has been cloudy after work so I did not get a chance to take any photos until today.  It has been exactly 1 week since I put the pump in the pond.  To my surprise the water was already completely clear:


I did not expect it to clear so fast.  I haven't actually checked the pond since Monday so it may have been clear for several days already.  Next year I'll have to take a photo every day!

I took a few other photos as well.

Pond with biofilter.  The grass is some type of pond grass that I got from a pond up in the mountains.  As you can see the biofilter had been overgrown with Himalayan blackberries, which I cleared away for the photo (and kind of beat up the pond grass in the process).


Biofilter.  The short piece of copper pipe comes from the pump in the pond.  I needed a stiff U-shaped piece to hang in the top of the large white PVC.  The black pipe is connected to my drip irrigation system.  It trickles a tiny bit of water every time I turn on my drip system (once a day), to keep the pond full in the summer.  We normally don't get any rain between mid July and early September.


Side view.  You can just make out the cleanout at the bottom of the biofilter.  I did open this once but the water was clean so I haven't tried it again.  I have had the biofilter & pond for about 10 years.


Another view. 


Pacific chorus frog tadpole eating algae.


Water boatman, in center.


Tadpoles feeding.
 
Emerson White
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Location: Alaska
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Absolutely beautiful. If you are trying to keep it more natural however you may want to replace the copper. Copper is death to the more frail crustaceans that form a good part of the food web in a pond.
 
Dave Miller
pollinator
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Location: Zone 8b: SW Washington
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Emerson White wrote:
Absolutely beautiful. If you are trying to keep it more natural however you may want to replace the copper. Copper is death to the more frail crustaceans that form a good part of the food web in a pond.



Thanks for the tip.  I used copper because it was the right size.  Originally I just stuck the 1/2" rubber tube in the top of the PVC feed pipe, but I encountered two problems:

1. Raccoons would mess with it, pulling it out of the PVC and sometimes onto the ground, which caused all of the water to be pumped out of the pond onto the ground.  If you look closely you can see tiny teeth marks in the rubber tube.
2. Over time the rubber tube would crimp at the bend point, shutting off the water flow and putting a strain on the pump.  I actually had to put some kind of stiffener at every bend point.  I should probably just replace the rubber tube with PVC or with stiff drip system pipe.  But I need to make all the connections before I put the pump in the pond - once I set the pump in the pond I cannot see anything because of the suspended algae!

Also looking at the photos just now I see that I should have used my polarizing filter!  Maybe I'll try again tomorrow.
 
Neal McSpadden
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Emerson is completely right about the copper.  What usually happens is that the bacteria that convert the ammonia to nitrite and nitrate lower the pH.  The low pH then dissolves a bit of the copper, which then poisons the aquatic animals (crustaceans, fish, etc).

Looking good though!
 
Dave Miller
pollinator
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I was up by the pond today and took a few more photos.

I think this is called a "boatman".


Pacific chorus frog tadpole.


More tadpoles.


Overview.  In the lower left am experimenting with a tray of mud for butterflies.  The idea is that the pond overflows into the tray, keeping it moist.  I have a connection to my drip irrigation system which puts water into the pond.  However I realized today that I need to push a little more water to the pond so that it overflows.

 
                              
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Great work! The filter seems to be working magnificently. I hope to have a similar set up...someday.

One suggestion: Make the pond larger! 


Also, is it possible to create a natural waterproof barrier with clay? Or is a thick pond liner required?
 
Dave Miller
pollinator
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I cleaned a bunch of leaves & muck out of the pond today and saw what looked like giant tadpoles. However their legs were not in the right place to be tadpoles. I asked the google what they could be, he thinks they are newts. I have only seen 1 or 2 newts in my yard ever, so it is cool to think that they are reproducing in my pond.

Here is a very immature one, about an inch long:



Most of them are 3-4 inches long. I think there are about 8 of them.

I used the muck on some plants and in my compost, I am sure it is full of microbial life.
 
pollinator
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Raccoons have been enemy number one this year. I set up a stock tank with a pond pump/ filter. It knocked it on its side and all the water pumped out. I since added an autofill system and put a grate over the tank.

I had a dead legless chicken and a dead headless chicken in my chicken coop. A racoon grabbed them from the outside and tried to pull it through the 1" chicken wire. I since added 1/2" hardware cloth around it.
 
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