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My pond biofilter

 
Dave Miller
pollinator
Posts: 437
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. 
 
Neal McSpadden
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What size is your biofilter?  From your drawings, it looks like you'll need more filtration.
 
Dave Miller
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The biofilter is around 40 gallons, and is plenty big - I'll be posting pictures as it clears the water.
 
Jeremy Bunag
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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.
 
Emerson White
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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
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Location: Zone 8b: SW Washington
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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
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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
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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.
 
wayne fajkus
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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.
 
Margaret Todd
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I don't know if you are still active with this thread but thought you may be able to give me some advice.  My husband and I are transforming our 24 ft. diameter above ground decked in swimming pool into a fish pond so we can be a bit more independent food-wise.  My husband likes feeding the fish; they know what's happening when he shows up and come to twirl in front of him for their food and are confident enough to make big splashes.  When it's beastly hot or raining or cold they stay in the depths.  

The pool/pond is very green and murky.  The algae problem needs to be addressed.  I want to make a bio-filter of two 55 gallon food grade plastic barrels we bought from the local co-op and a bog filter using a 5 foot diameter, 1 foot deep kiddy pool.  If my calculations are correct we have between 50,000 to 55,000 gallons of water that needs filtering. The water level is normally about 4 feet deep but we have the egress blocked so when it rains a lot there can be 5 feet of water in it or more.   I have a submersible pump covered with a poly-fil batting wrap filter over a milk crate that moves that much water every eight hours; right now we are using it as a fountain to increase O2.  I can't find the information as to how big a bio-filter would be needed for that much water.  The calculations I saw were beyond me. Also I have several strengths of Hydrogen peroxide to help with the algae overgrowth and instructions to dilute it down to 3% for fish safety.

I can use rainwater runoff from the garage to fill the pool/pond when it's dry too long which probably needs a pre-filter for any roof or other debris.  Our county buys its water so I am not using that to top up the water level.  It has rained sufficiently to refill it so far.  We have one small mouth bass, many Bluegills, and several fat catfish.  Paul has "fed" the bass 5 pounds of minnows occasionally.  We plan to eat the bass and bluegills this fall though we could leave them overwinter - they did fine last winter even with an occasional layer of ice.  We have a bit of an ecosystem with the frogs laying their eggs and the flying insects laying their eggs on the surface of the water and other critters that visit.  Some frogs manage to escape the fish who really like the frog eggs and tadpoles.  Paul tried to rescue a frog he thought was stuck in the pool but it came back.  I have rescued snakes but rarely. Years ago a squirrel must have fallen through the ice and drowned, found in the spring.   A heron stopped by to check us out but I think the pool depth discouraged it from fishing and now the birds would be confronted with the sail shades.  My compost buckets produce maggots we can feed the fish and I've made a simple non-smelly maggot farm which is strung over the water.  When the maggots try to go down through the holes in the bottom as they would into the ground they find fish waiting.  I've made structures from plastic lattice for shade and so smaller fish can hide in them giving them some chance of avoiding the bigger fishes hunting.  The sail shades positioned over the water provide some relief from the blasting sun and tall trees also shade the pool in the late afternoon.  The lattice structures float loose providing some shade.  Initially, the only shade had been under the Rubbermaid steps.

I saw an article about using window screen instead of the poly-fil over the crate the pump is housed in. That sounds much easier to clean and nicer than trying to clean the algae soaked poly-fil.  I was using the barrels for water for the garden but think this is less problematic and way more effective and necessary for the pool/pond.  My husband advised that the barrel rim was necessary for strength and to prevent cracking. He pulled out the reciprocal saw for me and I managed to make the starter hole and used the saw to open the tops of the barrels. They already have holes I made for the rainwater collection kit from Walmart (available online as well) which holes I think I can use for the proposed filtration system with some modifications.  I like the plans which call for the water coming in the top down to the bottom and filtering up to the overflow.  That only requires one pump push up.  I plan to use hose to move water from the pump to the barrels; the pump came with attachments for various uses.  I will need more lava rock, a grate to keep it off the bottom, pebbles and scrubby filter discs for the large barrels and pebbles, pvc and plants for the bog garden.  The pool deck is somewhat old as well and so we plan to reinforce it with outdoor rated 3/4 inch plywood under the bog garden.

Thanks for letting me share our plans and concerns.
 
Dave Miller
pollinator
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Location: Zone 8b: SW Washington
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I don't have any fish in my pond and I don't put anything into it other than water.  But there are lots of tadpoles and small life in the pond that just showed up.  It is under trees so it gets a lot of leaves in the fall, which I clean out every few years.

The waste from your fish plus uneaten food will increase the amount of suspended algae.  So your proportion of plants will probably need to be higher than mine.

I know that people do calculations to determine the size of the biofilter based on the pond size, number/size of fish, etc.  But I would probably just make it a little bigger than you think you might need, and/or make your filter expandable by daisy chaining several drums together or something like that.

I pretty firmly believe that the plant roots are way more important than the lava rock or biofilter balls etc.  I don't think it matters much whether the plants are in the biofilter or in the pond itself, as long as oxygenated water is moving through the plant roots.  So you might think about ways to be able to keep adding plants until the algae disappears.

Here's the intake filter that I use with my pump:
https://smile.amazon.com/gp/product/B0024EFYU6/
Yours will obviously need to be bigger but I like this general style.  I only clean it once a year.  Note that this filter does not filter suspended algae - it just prevents the pump from getting clogged.

As you mentioned, shading the pond will be good for water quality and to keep from cooking your fish.

I also encourage you to include some moisture-loving flowering or edible plants in your pond and/or biofilter.  It is great to have a "garden" in my pond that I don't have to worry about watering even on the hottest days or if I'm on vacation.  And of course the water has a lot of nutrients that the plants like, so no fertilizing either.  You just need to be able to adjust the height of the pot (or the water) to the plant's liking.  I have drowned a few plants by not getting that right.  And of course if you're going to be gone a long time, you'll need an automated way (or a neighbor) to top it off.  My drip system puts a little water in it every day, but you could also use a float valve.

Also a word about duckweed - I once put some in because I thought it would keep the water cooler.  Within days it covered the entire pond, and the frogs etc. seemed to be struggling to navigate through it, plus it made my pond just look like a lawn.  So I used a strainer to strain it all out.  It took a long time because you have to get every single plant.

I have attached some more recent photos without the "Photobucket" watermark.

DSC_0018.JPG
Immediately after putting the pump in the pond in early summer
Immediately after putting the pump in the pond in early summer
DSC_00193.JPG
The next day
The next day
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MyBiofilter.JPG
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I need to remove the filter material from the drawing. It doesn't really do anything and it was a big pain to remove when it broke down after a few years.
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[Thumbnail for 14214636627_c1799dd5a3_k.jpg]
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