Erik’s Swimming Pool to Pond Conversion

Welcome to my swimming pool to pond construction web page. I thought I would share with you a project I undertook converting a swimming pool to a pond. I moved into a house with an swimming pool near Portland, Oregon. I was always fond of ponds, and in fact, had built my first fish pond at my previous house. I always wanted a larger pond and here was my chance. Feel free to browse through my pages. If you have any questions, feel free to contact me, I’d love to hear from you.


The Swimming Pool

I started with this 24′ x 16′ x 7′ deep Doughboy pool. The swimming pool had a plastic liner. I cut out just the bottom portion of the pool liner and revealed the dirt bottom. Nervous that years of chlorine might be in the side liner which was to become the side of a flower bed, I covered the side with sheets of plastic.

Original Swimming Pool

The New Pond

The pond took me about five months of pacing myself to complete. I worked about an hour every few days, along with maybe an extra effort every couple of weekends. My goal was to fill the pond and get the flower beds planted in January. This allowed me to get pretty winter plants (so the pond would look nice in the winter). It also allowed the water to acclimate before things warmed up in spring and summer. Here is how the pond looked as soon as it was completed:

New Pond

Clay Model

I made a clay model to scale, 1/4″ = 1′. This allowed me to visualize the contours and shape of the pond. It helped me see where I would fill in dirt and sandbags to make multiple levels of steps within the pond.
Model of Pond


I used four truck loads of dirt, 400 sandbags, and countless hours of wheel barreling to fill in the swimming pool. Sandbags were used to help build multiple levels of pond depth. As I approached the height I wanted, I took my time and made sure I was making a perfectly level sandbag top edge. In the picture above the outer ring of sandbags is the edge of the pond (to be covered with rock). The dirt remaining to the edge of the swimming pool will become flower beds.

Sandbags to give the Pond Structure

Initial Fill

I used a 30′ x 34′ piece of EPDM pond liner. I’m starting to pull it over the pond in this picture.

Initial Fill

Empty Pond

Adding Rock Edging

After filling the pond I used about 3 tons of Camas Gray 4″ A-cut rock and round 35-75 lb boulders to build the edging. I did this while the pond was filled so I could see how things were looking. When I was done placing the rock, I drained and rinsed the pond. This picture is after draining. You can see I’ve already started planting plants around the edge.

Areal View

Biological Vegi Filter

I was very concerned about having such a huge amount of water go bad on me that I planned on a pond filter. I didn’t want a huge ugly algae mess. I spent considerable time researching filters. On my previous home’s pond, a smaller typical yard pond, I built it like an aquarium — with an underground gravel filter with PVC pipe running through it. It worked fantastic and I had perfectly clear water for years. But someone warned me it will be hard to clean. So this time I used the same principle (since it worked so well the first time) but I built it external to the pond. In addition I had now learned about the vegi-filter concept which incorporated plants.

Vegi Filter

The basic idea for my filter is to pump water to the filter, have the water purculate up through the gavel and plants, and then let gravity bring the water back to the pond via a spillway. I used one foot of gravel and an additional foot of water above for the plants. Finally, the water returns to the pond with gravity through a robust spillway that is safe from racoons and clogging from leaves.

Filter Construction

I used 8′ landscape ties and 3/8″ rebar. The whole thing is 16′ x 2′ x 2′ which is approximately 500 gallons and 5% the volume of the pond. Concerned it would be hard to insert the rebar, I cut and overlaid all the wood first without the rebar. Then I used a plumb bob and string to mark each piece where the rebar goes. I took the whole thing apart, drilled the holes for the rebar, and put it back together. (Make sure the holes are a little big — otherwise it’s a royal pain to fit the landscape ties back over the rebar.)

Base of Filter

Adding the Gravel

Next I added 1 foot of gravel, connected the pump and plumbing, and added a few 79 cent bunches of watercress to start growing in the water. In 2001 through 2002 I added six plants of mint and let them grow as they will. The mint is doing best had has overtaken the watercress. The last picture above shows the mint. (Today I have given up on the watercress and mint and just use water hyacinth in the summer.)


When I built my first gravel filter, I read somewhere that it should take 45 minutes for the water to flow through the filter to maximize the bacterial action. This is very slow. Nice because it means you can get by with a smaller, cheaper, and more efficient pump. Unfortunately I don’t seem to be able to regulate my water to go that slow. I noticed my filter fills in about 20 minutes.

Cleaning the Filter

Everything kept my pond crystal clear for so long that I honestly didn’t get around to cleaning my filter for 5 years – then I figured it was time. I was worried what I might find. To my surprise when I removed the gravel to rinse it, I found it only scummy along the top. Most of the gravel was rather clean. Honestly, I think I could have gone another five years w/o cleaning. Note that this is far better than the commercial filters you’ll find for many times the cost. Ask them how often you should clean them. You’ll find they need cleaning about every week.

Pumping water from the Pond

Pond water is pumped with this pond sump pump up out of the pond, under my deck, and over to the filter on the side.

Here is a movie how it works. This is in QuiteTime format and may need you to download the QuickTime plugin.

Pond Filter Movie


I reworked my outflow plumbing recently to add a T-connector with a threaded plug on both the inflow and outfloor pipes. I placed these at the lowest point in the plumbing (which is just under the filter). The next time I want to clean my filter I will unscrew these plugs, let the water spill onto the ground, and stir up the gravel. This will let me flush the gravel clear without having to remove the gravel. (BTW, I have done this now once and it was very easy.)

I don’t quite understand why the filter doesn’t need cleaning except for every 5+ years. My guess is I’ve properly sized the filter and the whole system is nicely balanced.

Pump and Plumbing

PumpAlthough I started with a Cyprio 2206 (2200 gph) pump, I have since replaced it with a smaller, magnetic 1200 gph pump. I did this because I noticed I was always turning down the 2200 gph pump to try to get the water to take at least 20 minutes to run through the gravel. The magnetic style 1200 is also quite a bit more efficient. The pump is in a pump cage at the bottom of the pond (at the 4 1/2′ depth.) The cage is wonderful. I think it would indefinately keep the pump from clogging. I pull it up about once a year to wipe off leaves and plants.


From the pomp the water goes via a flexible 1 1/2″ tubing to hard1 1/2″ PVC near the pond edge just under the water’s surface. From here the 1 1/2″ PVC takes the water under the deck to under the filter. Before the PVC enters the filter, I have placed three very useful accessories. First, there is a T’d off hose valve as the PVC crosses over the pond edge at its highest point (hidden in the flower beds). Second, there is an inline ball valve to control the water pressure and speed. Third, there is a T’d off and plugged drain at the lowest point in the PVC run. These all allow me considerable flexibility in controlling the water, draining the pond, draining the filter, and draining the PVC pipe itself.

The pipe enters the underside of the filter with a 1 1/2″ bulkhead. You can search for this on the web – they are hard to find in stores. This forms a water tight seal for the PVC to get through the EPDM liner of the filter. From here a little network of PVC pipe is embedded in the gravel with little holes. This allows the water to evenly disperse through the length and width of the filter. At this point the water fills up the filter from the bottom up.

Under Filter WebI am using 3″ black ABS drainpipe for the outflow from the filter. The water “overflows” into a 3″ wide ABS pipe sitting vertical in the middle of the filter. Water then falls down this 3″ pipe. You may have seen large dams us the same technique for their spillway. The water spills through this ABS piple, through the pond liner with a 3″ bulkhead (a rather spendy $50 piece of plumbing), passed a plugged T-fitting (for drainage), and then under the deck and up over the lip of the pond onto some rocks. Obviously, for gravity to work, the filter surface water must be at least a few feet above the surface level of the pond.

Filter Plants

Over the years I have experimented with several different plants for my filter. I tried water cress for a couple years – it would go crazy and spindly in the summer. I tried mint – it worked well but also would get out of control in the summer. Both of these had an advantage that they continued to grow in cold weather. But I have settled upon using water hyacinth during the spring, summer, and fall. I go ahead and purchase about $40-$100 worth of water hyacinth every spring. It grows like crazy and filters fantastic. Unfortunately it dies every fall when the frost returns. During the winter I have sometimes let the filter run without any plants (and in fact that is what I’ve done the last couple of winters.)


I took my time and slowly, over a period of months, introduced some fish. I started with the cheap feeder fish. Then comets (which are nice and bright orange), then shubunkin (which are my favorite, they are like little koi), and then some koi. The fish have been multiplying on their own. So I don’t know how many I have. Sometimes I seem the school together and it looks like I have about 20, but there are always babies if you look in the nooks and cranies. I never feed my fish and they are looking very healthy and growing. They are eating the algae, the plant roots, and I suppose little bugs and stuff that find their way into the pond. (When I try throwing fish food in the pond, the fish totally ignore it. I guess they aren’t used to it.)


I haven’t ever used any chemicals or medication. Never use salt. With this size of pond, the amount of chemicals I would have to use is huge, and I didn’t want to make a mistake. So I don’t bother. All seems well and happy.

Costs and Statistics

These are estimates from memory:

  • Pond 11,000 gallons estimate, Filter 500 gallons
  • Fill dirt, $400 (4 truck loads)
  • Sand bags, $100
  • Liner (for pond and filter), $750ish (I think it was .65 sq. foot)
  • Rock, $200
  • Pump, $250 (first one died for some reason, so I’m on a second)
  • Plumbing, $200 (that flex tubing is expensive)
  • Landscaping ties, $100
  • Plants, trees, shrubs, flowers, $600
  • Gravel delivered for filter, $60
  • Occasional replenish of water cress ($10) from Safeway
  • Occasional replenish of water hyacinth ($40) from a mail-order company.

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