I can't claim anywhere near the volume of your pond (just a little pond envy there) but even with my 100 gallon Skippy I had many of the same concerns. I cleaned out four Dollar Stores of scrubbers before I came to my senses. The fact is you can use just about anything so long as it has lots of surface area that can be exposed to circulating water. The list of bacteria homes just on this forum has gone from the scrubbers to floor polishing pads to plastic spoons and forks and everything in between. Some materials have even been free.
I cover my pond every fall with plastic netting to catch the leaves. Maybe I should say I try to cover it. When the leaves are no longer a problem and the netting comes off, it is usually somewhat torn up so I roll the netting up tight and stuff it in the middle layer of the Skippy and it becomes a haven for bacteria. I've got about 7 years worth in there now. It scrunches up pretty well if you use some of those plastic ties. The netting is cheap when you get it at end of season sales. Scrubbies are not cheap if you use them in large numbers and somehow I find a few scattered in the yard every year.
I'm pretty sure you can find any number of things that will work. Even the plastic spoons and forks you could recycle after a few picnics and parties would do the job.
I agree you should avoid the stones. They would be a horror to keep clean enough to be healthy. It is just transferring rock on the pond bottom to the filter. It works for a while but not for long.

Hi,
Nice size pond you have there,lol! You can use the gravel and create a bog filter. As long as you install a backflush you should be fine. Inside your filter you need to create a settle chamber withn it by using cinder blocks and grate. You should have an empty space of about 8-10" and then place a grate and then the stone on top large stone first then small stone. All the debris will stay in this area. I would go ahead and plant your filter as well the roots of the plants not only will absorb the nutrients but as they grow the debris will stay n the bottom as well in the end the plants will create a mat of roots just cleaning you pond naturally. When you clean it all you will need to is backflush because you and empty chamber to flush out. Other options would be shaved pvc as well.

A good pump for you would be a mag pump, pondmaster 1200 or 1800 would do.

GREG

d'Lynn,

Is this planter going to be above ground? The reason I ask is that I have a filter on my koi pond that is a little larger then the one that you are talking about. Mine is 12'x 4'x 4' ft deep and 1200 gallons. Those are the outside dimensions. It is all above ground and it has been in use for 16 years now. I think you want to rethink your flow rate. I have a flow rate of 4000 gph that returns back to the pond by gravity with a 3" pipe. If you are going to go above ground then we need to talk about the construction of you tank.
Mike

Sleepless: I have a contact for scrubbies at-cost.., but it is still 'a-lot' of 'em [estimated at 10,000]. Gravel would be a permanent solution - just hard to clean.
- Greg: Good idea on the 'dead-zone' at the bottom., didn't think of that.., and i have just the thing to use for grating. - I was looking at a magnetic pump for this project.,and have a special 'cage' to house it in..,and will look into the PondMaster. Thanks for the tips..., and I added a back-flush valve to the design just last night - good idea.
- Mike: The planter will be all above ground except for the piping. I have read that the flow rate should be slow enough that it takes the water atleast 30 minutes to go through the biofilter. Guess that's not right? By 'construction' of the tank/biofilter.., do you mean the intended flow-rate? I can make the bio filter larger-as I have the room to make it the same size as yours 1200-1400 gallons. - I would love to push 4000gph.., if it's a rate that will effectively filter the water., giving the resident beneficial bacteria time to do their job.
1]What size is your pond?
2] What do you use for media in the biofilter?
3]Do you occasionally spike the biofilter with beneficial bacteria? - [At the start of Spring?]
The whole purpose is to stop the green algae bloom in the spring and keep the pond crystal clear.
- Thanks everyone - appreciate the thoughts., ideas and comments.

Let me talk about what I meant before I start to answer the questions you asked. At 800 gallons you have a lot of weight in the tank roughly 7,000 lbs. There is fairly little force pushing on the bottom, about 1.5 psi so the ground will not have a problem with that force. But the wood walls will have a lot force against them. You say you are going to use cedar garden post but you don't say how it will be built. So let me tell you how mine is built. I used treated 4x4's for the walls. These were put together like Lincoln logs. On the bottom layer the corners are lap joints so there is a 4x4 going all the way around. Then there is a 4x4 on top of this on the 12' length and then a 4x4 on the 4' width so there is a 3.5" gap between each layer of 4x4 all the way up to the top where the top layer has lap joints. In each corner there is a .5" threaded rod going down through each 4x4 to hold all the 4x4's together. There is also two more .5" threaded rod on each of the long sides holding those together. Then there is 1/2" plywood lining the box with a liner inside that. Within two days after filling the tank the bottom of the long sides had bowed out at least 2 inches in the center. After about a year the long walls on the bottom had bowed about 4 to 5 inches. At that time I decided to put two 2" pipes set in concrete on each of the long sides. This stopped from bowing any more. But even with this there are some pretty good size cracks in the 4x4's after 16 years and at some point the 4x4's will fail.

Why 4000 gph flow rate? This gives me a twenty minute dwell time. Is this idea? No one knows for sure but this rate has been used for years with a great deal of success. Filters today are going to a much lower dwell time and they work somewhat.

My pond system is 19,500 gallons including the water in the filters.

The first 12 years that I ran this filter it had 2 ft of lava rock held above the pipes on the bottom that had holes in them to distribute the water. On top this there was one roll of spring flow and 36,000 ft of 1/2" wide PVC plastic strapping. Then there was 4 inches of polyester pads. This filter was cleaned once during that time. At that point in time I removed the lava rock and replaced it with PVC ribbon which is a machined product of 1/8" wide continuous ribbon. This filter currently has about 18,000 sq ft of surface area to grow bacteria.

No I do not spike the biofilter with beneficial bacteria as there is no need to do this. Currently there is no manufacture producing a beneficial bacteria with a bacteria that a good koi pond can't produce on it's own and maintain on its own. Granted it takes the pond years to do this. I have gone on here way too much all ready to continue to talk about beneficial bacteria. Depending on the type of pond beneficial bacteria is not only a good thing but a necessary thing.
Mike

Mine is 12'x8'x4'deep, contains around 12 cubic yards of 1-2" river rock. About a foot above main pond level, most of this filter is below ground. The bottom contains a foot of 4-8" river rock to create larger spaces. A manifold feeds 4 2" pipes on the bottom, drilled with appropriate numbers of holes to distribute 4000 gph evenly. Between the 4 pipes are 1" pipes drilled for an air bump. Each spring I shut off the water pump for a few hours and run 80 lpm air to stir things up, then drain the filter dry back through the feeder manifold. Filter pit is deep enough, with 4" drain, so I can gravity flow the discharge. There is a second manifold set about 6" under the top of the rock layer which gravity feeds through a 4" pipe to a third manifold that distributes the water back via TPRs and a distribution pipe under my rock necklaces. Any overage of water, a modest flow when my pump and skimmer are clean, overflows the filter back to the main pond. In winter I throttle the pump back a wit so all water returns via manifold. Some years ago MikeIL provided advice on this basic design, and it has kept the water crystal clear ever since. The pump runs 24/7/365 except for occasional maintainance of skimmer etc. There is no exposed water on this filter; it is planted in cattails, lizard tail, grass, and hosta all bare root. Local pond clubs visit because they heard of the filter that keeps water clear all year.

Pond complex 15,000 gallons: 10,000 koi pond; 1,000 settling chamber; 1,000 in filter (would be around 3,000 without rock); 3,000 lily pond fed from the bottom drains via settling chamber. 2 Sequence low-head pumps, one drawing from bottom drains and feeding lily pond is shut down for winter.

I second MikeIL's opinion to flow more water through. At 8000 gallons you should flow at least half through this filter each hour. Modern filters are seeing dwell times a fraction of what we're talking about here.

External BioFilter

Thanks for all the info.., and to answer a couple of the questions.
The end 'planter' biofilter will be approximately ten feet from the pond.., and the gravity fed 'over-flow' pipe [3in PVC] will have a drop of just over five feet back to the pond.

I have changed my original design to use 4x4 pressure treated instead of the cedar 3x4.., and to incorporate four fence post, metal pipes sunk at least two feet into concrete. [two on each 'long-side'.] Add a second mini-manifold at the bottom of the biofilter and will pump oxygen thru this new set-up - though I am not sure I will need it., as the pond is well aerated.

Considering the cost of all of this I was also thinking [which I do too much of.] .., I have about two hundred concrete pavers left over from several patio's that I installed - and were destined for some other project. They are roughly 9x7 x 2 inches thick. With just a couple hundred more I could build one massive/solid biofilter. These are the same pavers that were used to make the patio where this biofilter will be next too - so it'll 'match' somewhat to the surroundings.
I have never made anything like this.., but the idea is fascinating. Anybody here a brick layer, also??

There does not seem to be any consensus on what media to use in a biofilter. I have seen everything from river rock gravel., to a couple thousand plastic forks.., the round plastic pot scrubbers.., and plastic ribbon/strapping tape. One guy used Styrofoam packing peanuts - though I never heard how his fish survived.
I was originally going to use round river rock gravel mixed with small pea gravel and lava rock.., as I have a few tons of smooth river rock gravel. With a proper back-flushing set-up., I don't see any problems with cleaning. [except at the two inches, or so along the bottom where sediment would build up.]
Then I was going to use those round pot scrubbers - a couple hundred per mesh bag - as I could clean the filter in sections to help preserve the bacteria - but it will take thousands to properly fill the 'planter' biofilter. Very easy cleaning.
I am looking into the plastic strapping tape - but have yet to find a source., or pricing to fill this biofilter. ..,again, easy cleaning.

So I am still weighing the effectiveness of each possibilities. Any comments / ideas on this ?

.., and: I have a brand new 4000gph pump that I will use.., [ I original thought this was too much flow..] I will install a heavy duty ball valve to adjust the flow as needed.

Thanks again, everyone - for all the help. I have all of Feb to get this together - and will start the build in early March.

d'Lynn / Chelan Washington

The more surface area the better for the bacteria to grow in your pond. Lava rock is the cheapest way to do a bio filter. However lava rock is becomes extremly heavy as you get older, lol. Your scrubers would next in terms of surface area. Shaved pvc or springflow is probably the best in terms of surface area and extremely light weight.

In terms of the filter set-up when you are done you do not want to mess with the filter except first of the year. Clean it once and sit back and enjoy.

GREG

If you are thinking of using the pavers to build the tank you will run into more problems. The mortar joints on the paver walls will not take that much force. So if you are going to do this the tank has to be lined with some thing that is strong enough that it can distribute the force over the entire wall. Then you would have a problem in the corners to take the force away from the corners. I don't think that this will be do able unless you build the tank out of wood and then clad it with the pavers.

If you are going to use rock as a media you are going to want a method to clean it. You might also want to think about a drain in the bottom for cleaning purposes.

Putting any filter media in a mesh bag is never a good idea. The point with any media is to get fresh water to come into contract with it. Once it is put in a bag it is easier for water to go around the bag ten to go through it.

Yes Springflow and machined PVC have about the same surface but they are made from two different plastics. PVC has a surface that bacteria likes to grow on and then machine it so that that surface is now rougher and bacteria loves to grow on it. Springflow is made from polyethylene which has a very smooth surface that bacteria has a hard time growing on it.

Mike

If you don't have a bag to hold it in, what keeps the media from getting sucked down the biofilter drain or going down the waterfall?