Frank and Jan's Pond Page
Building Our Pond Filter
A Gravity Fed, Mechanical and Bio Filter
for About $100

Updated 1/07/01
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When we started building our pond in August 2000, I was concerned about the small in-pond pump and filter that came with it.  After reading some Internet pages from very helpful ponders, I adopted a design for our filter that would utilize a relatively large mechanical and bio filter media area outside of the pond using simple, everyday items rather than buying a pre-made filter.  I also wanted to avoid multiple pumps and the extra energy they consume, and didn't want the filter to interfere with the appearance of the pond in the corner of the yard.

Now, 2 months after its installation, I can consider the filter a success.  The pond is clear, with plenty of water flow, and the filter has been trouble-free.

Putting a filter outside the pond means you have to get the water to the filter, through the media, and back to the pond.  Some people use an in-pond submersible pump, pump water over to the filter, through the filter media and allow the water to spill into a stream bed for the return to the pond.  I couldn't do this without the filter showing above ground.  Another method is to use two pumps, one to pump water into the filter, and another to pump it back into the pond.  The third method has the filter in the ground, at the same level as the pond, and a pipe between the pond and the filter allows water to flow to the filter.  Then, a pump in the fitler container pumps water back out and into the pond through unobtrusive plastic tubing.  As the water is pumped out, water flows from the pond through the pipe to the filter.  A good website showing this concept is at xxxxxxxxxxx.  For ease of cleaning, I decided to use the horizontal flow method the website shows.  And using the math there, I determined that for my small pond, 2" ABS drain pipe would be plenty big enough to allow enough water to flow through it.

In addition to the mechanical and bio filtration provided by this filter, we decided to have a veggie filter also.  We're using another pond that will be stocked with a lot of plants.  The water will be pumped up from the filter into the veggie filter pond, and then flow down a 3' stream into the larger pond.

Shopping at Home Depot, I gathered the following materials:  1 Rubbermaid 28 gallon "tote" with lid ($9.97), 2 permanent "hog's hair" air filters for forced air units ($3.87 each), 1 plastic "light panel" ($7.97), 2 shower drains ($3.89 each), and enough 2" black ABS pipe to reach from the pond to the filter.  Later, I purchased some red lava rock from the local landscape supply place for $7.  I had some other "optional" expenses you'll see in the photos below, but they really weren't needed.

Here is the gasket from the shower drain positioned on a relatively flat area of the Rubbermaid tub.  You'll find the shower drains where the plumbing supplies are for installing a fiberglass shower unit.  They have ones for tile showers out of cast iron, but you want the ABS plastic ones that have the drain grate, a flange, two gaskets and a threaded nut. 

The gasket makes a template to mark the tub for the hole, as I did with the marker pen in the picture.  You can carefully cut through the Rubbermaid tubs with a utility knife if you are patient.  Make several light passes at first, gradually increasing pressure, and soon you are through the plastic.  Trying to cut through quickly could lead to the knife slipping, and cutting other things, such as body parts, which are considerably easier to cut than the tub!

Here's the shower drain installed into the tub.  A gasket goes on the flange of the drain (which is white, you can see the back side of it in the picture.)  Then the drain and gasket are pushed through the hole from the inside of the tub.  Then, another gasket fits over the pipe portion of the drain, and the large nut is threaded on.  You do need a large pipe wrench or channel lock style pliers to tighten the nut, but you don't have to go too tight.  If the plastic squeeks, STOP!  You can crack the nut if you overtighten it.  Its also important not to put any kind of pipe dope on this, as some of the pipe dopes can actually cause ABS plastic to crack later on.
Here's the inside of the tub showing the installed shower drain.  You could go through one of the other side walls, or the bottom, as long as the place you choose is nice and flat relative to the flange on the shower drain.
Next, I took some stiff cardboard and made a "pattern" of the inside of the tub.  Using scissors, I simply kept trimming the cardboard until it would fit down into the tub.  The large grate you see in the picture is found in the lighting section, and is used as a light diffuser for flourescent lights in places like schools (but don't take one from your school ... they'll put a note in your permanent record!)  It is made of a styrene plastic, which is easy to cut with tin snips, a band saw, etc.  I used the paper pattern to mark the grid with the marker, and then I cut it out.  I actually found tin snips to work better than my band saw (sometimes hand tools do work better, but don't tell Jan until I'm through buying all the power tools I want.) 
Here's a gird piece cut out to fit in the tub.  It doesn't have to fit exactly to the sides, or even go up as high as I have this one.  Realizing that meant I only used one of these light grids (I actually bought two) and I briefly thought about returning one to my elementary school to expunge that permanent record thing.  But I took it back to Home Depot instead.
Here are three girds in the tub.  And the pump, a Rio 1700 Power Head pump that I spent $47.50 on.  The two grids at the top of this photo are hiding the shower drain "inlet" into the tub.
Here you can start to see how the filter shapes up.  The permanent filter material goes between two of the grids.  I used three layers of the material to provide plenty of both "depth" and surface filtration for debris.  The lava rock will go between the bottom grid and the two top ones.  Lava rock is kind of controversial, and a lot of people prefer other materials like fiberglass insect screening, plastic pallet strapping, Bio Balls they buy in a store, etc.  The idea is to provide a place for beneficial bacteria to form so they can feast on the stuff you don't want in your pond.
OK, here's where I went a little crazy.  I made a manifold out of valves and plumbing fittings so I could direct the water out of the pond to different areas.  Obviously, this is an optional feature.  And these valves and fittings cost as much as most of the other stuff.  But Jan had a giant fish and snail sculpture (yeah, you read that right) that will spit water into the pond, and I wanted to divert the rest over the side of the upper "veggie filter" pond when it is too windy to allow the fish to spit.   We had to use the giant fish and snail sculpture because our kids thought it was too gaudy for us to actually use.  Embarrassing your kids is the only way you can get them back for terrorizing you when they were 2 years old.
Here Dennis, my daughter's boyfriend, is helping me install the other shower drain in our pre-formed plastic pond (in beautiful natural black, of course.)  The 2" ABS pipe should be level or slope down to where the filter is recessed into the ground ... if you have a high spot in the piping, any air can collect there and restrict flow into the filter (and it would be nearly impossible to get it out of there.) 
Here Dennis is topping off the lava rock in the center section of the filter.  You can see where the shower drain and black ABS pipe is at the lower end of the Rubbermaid tub on this side.  The "veggie filter" pond is on the right, with a few plants in it.
This shows the finished filter, in the ground, hooked up and ready to fill with water when we re-fill the lower pond.  On the left would be the shower drain "inlet" to the tub (which you can't see in this view ... its in the space before the furnace filter material).  This area before the furnace filter material forms a kind of "sump" for heavier stuff to fall into rather than collect directly on the filter material.  I used short pieces of the light grid material to hold the vertical grids in place ... you can see two in that "sump" space if you look closely.  Another two are on either side of the pump at the right end of the tub.  I used aluminum wire to light wire the short pieces  to the upright grids, and just allowed the pressure of the lava rock to then hold the other ends against the tub walls.
We filled the pond, plugged in the pump, and sat back.  In this view, you can see we have a lot of landscaping to do, but when we close the lid on the filter (which you can see against the block wall back there), you don't even know a filter is there.   The fish and snail sculpture is on the right, and has been moved now to spit into the little stream bed between the upper and lower pond (there's so much movement of water in the upper pond that we had to divert some of it!)

Landscaping around the Pond

January 7, 2001
Jan decided she wanted a way to walk out to the pond when it rains, without getting muddy.  I'm usually the one to do outdoor landscape design, since I once worked in that business (over 20 years ago!)  But she came up with the idea of using flagstones with groundcover growing in between.  Here, we've excavated the area the walk will go in, and have added some of those self-aligning retaining wall blocks around the pond area (note that they extend around the front of the pond and back around the right side.)
A layer of sand was put down first.  Since we don't have to worry about frost heave in sunny California, we only need enough sand to set the stones easily so they won't "rock" as you walk on them.  That's only an inch or so.   Here, our daughter Kris is brushing more sand in-between the stones as part of the final prep for planting the ground cover in the cracks between.  Abby, our mini-schnauzer, is sniffing around like usual. 
Here's the walkway with sand between the stones.  The area to the right will be grass like the area on the left (we'll install sod there next weekend.)  The grass on the left looks bad in this picture, as there is quite a bit of dirt on it, and the cooler weather means it grows slowly and doesn't recover quite so fast.  This spring we'll "overseed" it.


Pond Filter Links

Norm Meck's Article on Horizontal Filter Flow is the site where I first got the idea for a horizontal, gravity fed filter.  He has the flow capacity of pipes listed so you can design one for your needs, and some info on how much bio media to use.  This article is really for koi ponds, which are larger than our little ones here, so I just scaled the formulas down.

Leslie's Puddle has information on an even more simple, elegant design for a pond filter if you can have it sitting on the side of your pond or stream bed.

Skippy's Koi and Pond Page has this article on building a bio filter for a larger pond than I have.  But the concepts he covers in the article helped me design my little filter.

JJ's Ponds features another filter that uses gravity feed or a siphon effect.  He has separated out the mechanical, biological and veggie filter into three separate units for his larger pond, but again, I adapted some of what he used to build mine.

JD Stone's Pond Page has a table of links to other filters made by ponders.

Great Pond and Water Gardening Books

Clicking on the picture or link will take you to, where you can read the reviews by other readers, get the ISBN number if you want to get the book at your local book store, or just see what other works the author has written.  You're under no obligation to buy, of course,but any purchases from when you click through helps support amature web pages like this one.

The Pond Doctor is our favorite.  While it has little on filters, its a great all-around resource for ponding, including how to deal with algae, identifying the right plants for your pond, etc.

Water Gardening Basics has been a great help to us as beginners.

Plants for Water Gardens helped clear up our questions on what would grow in our area.  Helen Nash is a great author on this subject (she also wrote our favorite, The Pond Doctor featured above.) lists hundreds of books on Water Gardens, but I've only listed the ones I am familiar with.  To see what else they have, click on the graphic below to get search results.  Use the "Back" button on your browser to return here.

Click here - search all of
for books on Water Gardening

My Other Obsession ...
When I'm not helping Jan with the pond (mainly by staying out of her way!) then I'm building my boat, Aslan.  See my boat building page by clicking here:  Frank's Weekender Project.  You can also Email Me by clicking here.

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