The Ultimate Koi Pond




Introduction: The Ultimate Koi Pond

This is a guide to constructing a koi pond for your garden or yard. I designed this pond and the layout of our front yard in order to visually connect the house to the street and protect our house from traffic. We (my fiance, future father-in-law, one friend and myself) completely transformed our small front yard with garden walls, walkways, new stoops and a wonderful koi pond.

Here, I am going to share how we built a custom concrete pond that will last forever, protect the fish through the harshest of winters, provide easy maintenance and beautify your home.

We expanded our living space outside and are able to enjoy the pond year round. The pond provides extra seating in the small courtyard, visual interest and soothing sounds of running water. While sitting on the ledge you are able to sit and look into the pond and entertain your guests.

This project took a few weeks to complete. As you can tell in the photos there were many other projects going on in the construction of our new yard. In order to complete this project, moderate construction skills and knowledge are required but by no means do you have to be an 'expert'. The most difficult aspect is having access to the concrete forms and knowing how to properly set them up.

This instructable can be taken and applied directly, or the ideas and methods can be used to influence a variation of this design/process of your own. Good luck and enjoy!

Step 1: Koi Pond Information


I just want to touch on some of the basics of koi and building a pond. I did a lot of research before designing and building our pond. I have found there are many myths out there about koi and want to dispel a few of them here. Koi are beautiful fish (in the carp family) that can live for many years if properly cared for. The better the environment you build for them the longer they will live. As you will discover water quality is key in keeping koi healthy.

Myth 1. Koi are expensive.'
It is true there are koi fish that go for thousands of dollars. Most cost 20 bucks or so and on up. You don't really need many fish, as we found out they BREED like crazy. So only buy a few to start. I recommend buying from a koi farm and not just any pet or garden supply store. You will get better quality fish in health and they are often cheaper at a breeder. By speaking to the breeder we gained a lot more knowledge of koi and learned about all the different types and colorings.

Myth 2. Koi ponds need to be large.
'''A general rule of thumb is one inch of fish per 10 gallons of water.'''
You can make a pond any size but you do have to be careful of over crowding in smaller ponds. I often heard people say koi only grow to a certain size based on how large your pond is. This is false. as long as you have healthy water quality and feed them they will grow to any size. The more you feed them the more they will grow, these fish eat nonstop. But with this in mind you have to determine what is right for you and your pond, such as how many fish you would like to have. Over estimate because of breeding and you will probably want more than you plan on.

Typically A koi pond should be no less than 1000 gallons (ours is around 2000 gallons). Ideally, you want to change the water twice a year (spring and fall). We aim for fall since the water will be good quality for the winter, therefore, putting less stress on the fish during the cold months. You will see further in this project how we installed a valve in the bottom of the pond to provide easy clean out, making maintenance fairly painless. There are a ton of water treatment options, filtering and pumping systems one can buy. As you get more involved in the hobby of koi ponds you can decide what is best for you. We started very simple expecting to add more later, though so far we haven't needed to. The pond stays crystal clear with the simple filtration system we started with, which is explained later. It is important to note that even though your water may be clear, it does not mean the quality of water is healthy for your fish. The 4 main water quality tests you should do regularly (especially before putting fish in your pond and again a day or two after the fish are in the pond) are PH, KH, Ammonia and Nitrite.

Step 2: Design and Redesign

Design Process:

Just how you measure twice and cut once, plan your design two, three or ten times. Your first thoughts or ideas usually are not the best. I know what I originally thought would be perfect for the front yard and pond would have fallen short of the final design we built. Below are some of my original designs that we didn't build.

Idea: Here is one technique to help physically visualize the pond and walls; take stakes or rebar and place them where the walls will be. Then run string lines at the heights of the walls. Do this and view the area up close, go down the street or stand and view them at a distance. See what works for you and looks right in your environment.

So draw and draw some more, have fun with it because planning is a great way to build anticipation for your project.

Step 3: Overview & Tools

Here is a general list of tools and materials used in the construction of the pond.

a. Digging tools; spades, flat shovel, tamper (a backhoe would be nice too!)
b. Measuring tape
c. Hydraulic rebar cutter
d. Impact drill or Hammer drill with lots of masonry bits
e. Reciprocating saw or Sawzall
f. Rebar tire gun and wire
g. Cordless drills
h. Square, one large and small
i. Hammer & rubber mallet
j. Caulk gun
k. Box cutter
l. Level, 6ft and 2ft
m. String line
n. Clamps, quick grip clamps and vice grips
o. Pvc handsaw

1. Wood & masonite
2. Metal forms and ties
3. Rebar
4. Stone
5. Pvc conduit
6. Pvc pipe
7. Metal shut-off valve
8. Styrofoam block & blue foam strips
9. Masonry screws - tapcon
10. Wood screws & nails
11. Caulk - waterproof rhinohide
12. Rubber seal - long rubber strips
13. Concrete
14. Concrete dyes & texture
15. Clay pot
16. Cinder blocks & 2' x2' slate pavers
17. 1500 gallon fish pond water pump
18. Flexable tubing for pump
19. Rocks & water plants
20. Koi

Step 4: Preparing Footers and Base


The first step to beginning the construction is excavating and preparing the site. I initially used a laser level to find all the elevations on the property and rework the grading on the front of the property.

Excavation for the footers was made easier by digging with a small backhoe attachment on a skid loader. On this end of the front yard the road grade tapers off which made the depth for the footers here a little more shallow. The footers were excavated at a depth of 32" at the deepest end (towards the bottom in this photo below).

Stone was then back filled to give a solid base for the concrete. String lines were put up to set the forms for the footers. We used 2" x 6" and metal stakes for the forms.

Step 5: Frame and Rebar for Footers

Step 2:

The footer frames were set up with 2"x6", 2"x10" and layered masonite for the curve. Rebar was then laid out and tied together with the rebar gun. The rebar was placed on top of rebar chairs (rebar blocks could be used as well) to keep the rods in the center of the concrete pad during the pour.

By using the hydraulic rebar cutter the rods could be cut to specific lengths. #3 size rebar (.375") was used in the slab. During the pour, the footers were poured first then the slab of the pond. It was all done in one continuous pour.

Step 6: Poured Footers

Step 3

During the pour #4 (.500") rebar was placed into the wet concrete. Later more rebar for the walls will be tied to these bars, hence physically connecting the rebar of the walls and the footers.

Right after the pour the rubber gasket was inserted into the concrete slab. As mentioned before this will keep any leaks from occurring where the walls will meet the slab. You can see half of the rubber gasket is protruding from the concrete slab. The half which is visible in the photo below will be encased in the wall during the next pour.

While the concrete was setting up, the wood forms were removed allowing the concrete to evenly set and keeping the concrete from sticking to the wood.

Step 7: Setting Forms for Walls

Step 4:

After the footers were set up we could prepare more rebar and place the conduit for the electrical outlets. By using the impact drill with a 16" masonry bit I was able to drill holes into the concrete of the footer and insert the tall rebar seen in the photo below. The rebar was banged in using a rubber mallet and a wood block. Later on, more rebar will be added and tied on for more support.

Electrical conduit was tied to the rebar and set up to run electrical wire for outlets. A sweeping elbow was used in the far corner to keep the wires from bunching up when pulling them through.

Before setting up the forms (which are laid to the side in the photo below) a chalk string line was struck. It was vital to keep all the forms aligned and to not have gaps in the forms. The forms are connected by cotter pins (see holes below in first picture) and metal plates which tie both sides of the forms together, keeping them parallel (see picture #3 below). These metal plates are encased in concrete during the pour. After the concrete is poured and set up, these metal plates are left protruding about 1" on each side of the wall (this is where they were connected to the cotter pin). Just take a hammer and hit them to snap off the end, they break easily and flush with the wall every time.

The form for the curve was built on site out of 2"x4", 1/2" plywood, masonite and luan plywood (see picture 2 & 3 below). The curve came from the circle which I had laid out for a small round patio in the center of this courtyard. By using the old method of a stake, string and a marker/pencil I extended the curve of the patio to the inside curved wall of the pond. Simply lay a piece of 1/2 plywood down level on the ground and strike the arc. Using a skill saw this was cut out of the sheet of plywood and became a template.

The curved wall had a base and cap of 1/2" plywood and 2"x4"s acting as studs every ten inches or so. A piece of masonite and luan plywood was screwed to the face of the support structure. Luan & masonite bend well and will give a smooth surface for the concrete to sit against during the pour.
Then both of these wooden forms where screwed into the concrete slab ( this wooden curve would be the weakest area during the concrete pour, making it most likely to have a blow out, so extra precautions are necessary to make it stable).Then 2"x4" bracing was placed on top of the wall connecting the two sides for the form. This bracing was nailed down into the 2"x4" of the studs to make it one structural unit.

Step 8: Concrete Walls

Step 5:

The walls are poured! All the forms were removed after concrete had set up. After a day or so we back filled with dirt . This was still about 4" below finished grade because we are going to put in a concrete pad (about 2") and pavers on top of that (about 2"). - but that is another project.

You can see the overflow hole in the wall. That was where the foam block was, shown in picture #3 in the previous step. The block was sandwiched in between the forms and screwed through them to keep it in place. It was also sitting on top of a few pieces of rebar acting as support from it being pushed down during the pour.

Much of the tough work is done!

Step 9: Prep for Wall Caps

Step 6:

Using 2"x4"s and 2"x6"s to make forms for the wall cap we plan to give it the appearance of thick slate on top of the wall. I looked into buying real slate caps; Pennsylvania Brownstone (I wanted a very traditional look as our house is 150 years old). I knew real slate would be expensive but was shocked at how much it would have cost (basically the cost of our entire project). So we will pour concrete and finish it to look like slate instead.

Start off by connecting the lip of the cap (2"x4"s) with masonry screws to the concrete wall. This will provide a base for you to connect the outside of the form. Screws are placed about every 8 to 10 inches. You can do this by taking the impact drill again with long a masonry bit and predrilling through the wood and concrete. Then screw the wood flush to the wall.

Then we used 2"x6"s to create the outside of the form. These too were connected by screwing through the lip and into the concrete using 6" long masonry screws. Again, this was done with the impact drill and screw gun as above.

You must check that you are staying level with all the forms, as the concrete will be poured to the top of the 2"x6". If they were not level it would be seen in the wall cap itself.

Step 10: Poured Wall Caps

Step 7:

The caps are poured! As they are being poured pull a board to keep the pour flush. Then come back with a trowel and small horsehair brush to do the finish (this won't matter much as we are going to apply a finish to the top later) but it is best to keep everything neat.

Step 11: Wall Caps Are Set

Step 8:

Remove the wall cap forms. Unscrew all the wood forms and clean up the edges of the concrete cap. Just take a paint scraper or flat head and knock off any small chunks that sometimes occur.

Step 12: Colored and Textured Walls and Wall Caps

Step 9:

First you need to clean the concrete before you apply the concrete grout mixture and color. You can clean the concrete by using a pressure washer and/or concrete grinder. We had to do both to get a smooth surface on the wall, grind first and wash second.

After that was dry a base coat was applied with a flat edged trowel to the wall and caps, which was a pure white grout. Then a second layer was added to the wall (cream in color). This was also applied with a trowel in circular motions to add a texturized look, similar to stucco. To knock down any really rough edges after the grout has dried use a rubbing stone trowel to knock down the edges.

To make the color for the wall cap you mix concrete colorant with water. Use any large household sponge (we used a big yellow sponge torn into a few smaller pieces) to apply it to the surface. Remember to wear latex gloves or your hands will be stained for a few days! I measured how big I wanted my slate to be and taped off grout lines with 1/8" heavy duty masking tape (fiber tape). You can use 1/4" tape as well depending on the look you are going for. Make sure the tape is pressed on well to prevent leaking. You can use a small plastic roller for this.

After you have your lines taped you need repeat the first step of applying the grout on the wall caps. Mix in the color of your choosing. When it's dry, (usually the next day), pull the tape. If you wait too long the grout will get too hard and you may have to use a paint scraper and chip away where the tape is. You may get a few spots where the tape pulls away at the grout, but in the end it makes it look more natural. You can take some of your color mixture to perform any touch ups.

Step 13: Dyed Wall and Building Platforms

Step 10:

The same color mixture process was used on the inside of the pond. I used the same color as the slate, but faded it up the walls. I wanted to darken the bottom of the pond to make the fish more visible. With all the water and plants the pond will become fairly darker anyway but the dye will just give it a little depth of color. For this step, the dye is just sprayed on with a spray bottle and then washed off with a hose. You should wash this out a few times to remove any chemicals. I had the drain open at this point to allow the water to escape.

Finally, when good and dry, you need to apply a concrete sealer on all of the finished surfaces with a paint roller. This will protect the surface from wear. Two coats should be applied. If done well this should not need to be reapplied for quite a few years since the pond is not going to get any foot traffic.

To build up platforms for the plants and fountain I used cinder blocks and slate. I used about 15 cinder blocks and about 15 pieces of brown slate (to match the wall caps). I stood the cinder blocks up on end and then placed the slate on top to hide them. Platforms at different heights were made for different types of plants. Some plants need to be at different depths in the water. This will also provide some visual interest when you look into the pond and most importantly will provide maximum hiding to protect your fish from predators. We in an area highly populated with wildlife and we do not want any animals getting a free dinner! You shouldn't worry about your fish hiding too much. After a few weeks they come out as soon as they see you, hoping to get fed.

Step 14: Build and Install the Fountain

Step 11:

Now you can have some fun! I wanted to install a fountain of some sort, but didn't want a fake waterfall. So i am going to use a pot for an overflow style fountain. It will look nice and still aerate the water for the fish.

I had to enlarge the hole at the bottom of the pot. I just used a flat head screw driver and a hammer to "chisel" away the clay and make the hole large enough to fit the tubing into (see picture 2 below). This pot also has lots of surface area inside and on the exterior because it is ridged. This will allow organic material such as algae to build up and clean the water. There are good and bad types of algae, these types that are in the constant flow of water actually prevent you from having a yuck green pond, so you want to promote their growth.

Attach the tubing to the filtration system. We used a 1500 gallon per minute water pump. (Our pond is about 2000 gallons). The other end of the tubing will obviously be in your pot. This simple filtration system has kept our pond clean, clear and healthy.

Step 15: Fill With Fish and Enjoy!

Final step:

Put in your fish and plants! Let the water run for a few days and acclimate the plants. Then add the fish.

When you put in the fish (they usually are purchased in a clear plastic bag, just how you use to win fish at the carnival) place the bag in the water and allow it to float for a few minutes This will cool/warm the water in the bag. This will allow the fish to become slowly acclimated to the water instead of just dumping them into your pond. Drastic temperature changes can stress or kill fish.

Now you have a wonderful pond that is easy to clean and enjoyable for a lifetime. Good luck!

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    12 years ago on Step 15

    Looks great im jealous but there seems to be too much direct sunlight which might attribute to the algae bloom.  How are the koi not eating the plants, will they eat anything they can fit in there mouth so big plants are ok???? Im leaning towards a nice breed of goldfish so i can have plants to help with balancing the pond, Water Hyacinth sounds like money it actually filters the water as well may want to check it out.


    Reply 6 years ago

    Water hyacinth is good at absorbing heavy metals and many other toxic things from the water. They'd be okay in a cool climate, but once you reach sub-tropical or tropical temperatures, your pond would be quickly overrun. They can double their mass in 24 hours. Perhaps the koi would eat them? I don't know. I do know that in Australia we have problems with water hyacinth blocking rivers and dams. Just one surviving piece can block a river again in a month or so, and you can never get them all!

    I'd look at azolla and duckweed - both would certainly be welcome koi food. The azolla grows nearly as fast as the water hyacinth, but is much smaller and the koi could definitely swallow them. Duckweed (Lemna spp.) are a bit slower, but even tastier.

    Water hyacinth are definitely beautiful, especially when they bloom.


    Reply 6 years ago

    My koi love to eat water hyacinth. We have a 2-level pond with a waterfall, and no fish in the upper level, so when the plants in the lower pond get their roots munched, we move them to the upper pond to regrow. The koi think duckweed is yummy too, but usually eat it faster than it grows. (I agree with the caution that water hyacinth can be a nasty invasive, but can't survive cold winters - it regularly gets down to -20C here (Ottawa, Canada), and water hyacinths seem to get killed by even a light touch of frost.)


    Reply 6 years ago

    At the risk of sounding hypocritical I've just collected some water hyacinth here in the Philippines. I've retired here, and it's all over the place. I will use it in my aquarium and for my aquaponics, feed young leaves to my rabbits, and mulch the rest for my garden. My aquaponics setup is very small, and it doesn't take much of a change in fish numbers to either starve the plants, or have too many nutrients - I can use the water hyacinth to clean up nutrients, and harvest more plants when nutrients are low.

    I probably won't have more than a square metre of water hyacinths at any one time. I've read that they oxygenate water too - I'm testing that now.


    9 years ago on Introduction

    Forgot to say what a great instructable this was! Thanks for sharing!

    Dr Qui
    Dr Qui

    10 years ago on Introduction

    Hi, for filter pump you say you use a 1500 gallon per minute pump, do you actually mean per hour? I am trying to work out the plausibility and numbers for a proposed pond. I would think at 1500 gallons per minute the fish would have to be permanently swimming away from the pump inlet.


    Reply 9 years ago on Introduction

    1500GPM?! Yowch! That'd be one polished concrete pond!

    camping crazy
    camping crazy

    10 years ago on Step 15

    That is awesome! But don't the fish go out the over flow holes?


    10 years ago on Step 15

    Impressive! Is the pot empty? You might consider adding some gnarly volcanic rock/other very porous nonreactive stones in it loosely (even just gravel). In addition to algae scrubbers, there's also beneficial bacteria that will aid in eating up excess ammonia. If it works as is then carry on, but might be something to think about :)


    12 years ago on Step 13

    Doesn't the cinder blocks you used on the planters messup your ph and leech lime into the pond?


    Reply 10 years ago on Step 13

    Koi like fairly alkaline water and can tolerate up to 9.0, so it might not be a problem. I used to put little concrete statues in my goldfish tank to keep the pH high.


    12 years ago on Introduction

    That's an awesome project.  I wish I had the time and/or money to build landscaping features like that.

    But I think you meant that you used a 1,500 gallon per HOUR water pump.  1,500 gal/min would typically require a 10" pipe.  I think a 1,500 gallon per minute pump would turn that 2,000 gallon pond into a whirlpool!


    12 years ago on Introduction

    Very nice instructable!  I too dream of building a pond like you when I have a garden one day.  I have had numerous aquariums in the past and now have a small 50 gallon pond on my balcony with a few comet goldfish.  It's been running super well.
    I think your fountian concept is great because it will oxygenate the water and it a very pleasing feature in the pond.  I like the high wall around the pond. it gives it character and prevents the fish from jumping out.  The overflow is a good idea, but I would put a netting accross it, because the fish do jump out.  Better safe than sorry. 
    Where did you hide your filtration?  In my pond design considerations, aesthetically hiding a large filtration unit ranks high on the priority list.  The larger the filter, the less maintenace is required.  The filter also needs to be located in an easy to access/clean location.  The filtering options you select will litteraly determine how much time you will need to spend maintaining, so I'm very curious what you have selected for that.
    In terms of water quality, I also monitor nitrates (N03), they are not as toxic as NH3 or NO2, but they do tend to accumulate to stressfull levels for the fish.  In addition, NO3 is a fertilizer and that is what leads to algae problems.  In the cycle of the fish poop, it satrts as toxic NH3 which gets processed in toxic N02 by one typeof bacteria, then the N02 gets processed to the less toxic N03 by a second type of bacteria. Both these type of bacteria require oxygenated water to operate.  The N03 accumulates at the end of the cycle and there are 3 (4) ways to deal with it:
    1- plants use it as fertilizer, so put fast growing plants that have their roots in the water (can be in a pot).  when they grow, they absorb/export the N03.
    2 - partial water change 10% every week or 2 to slow the accumulation of N03.  This would be more effective in maintaining water quality than 2 complete water changes/year.  When you do a complete waterchange,   you also eliminate all the useful bacteria that keeps you eco-cycle going.  It takes weeks/months to re-establish it.  This would be when the toxic NH3 and NO2 will spike until the tank is cycled and the bacteria equilibrium is re-established.
    3- there is a 3rd type of bacteria that absobs the N03 and that just releases harmless N2 (nitrogen = 79% of what's in the air).  But the challenge is that this type of bacteria needs a low oxygen environment.  So a traditional filter with high oxygenated water flow does not work well.  In nature, this type of bacteria lives deeper in the substrate at the bottom of the pond where there is little oxygen.  You can recreate this in a pond or an aquarium by having a deep sand bed.
    (4)- If all of the above is not done and there is a bit of sun, this is where the ugly algae bloom comes in to consume the N03.  It's nature's way of dealing with it to re-establish a healthy balance.

    So in all my experience, I learned that there is no need to fight mother nature with chemicals.  Once I understood the eco-cycle that I was trying to replicate at home, I could make sure that all the parts of the cycle where fulfilled and then enjoyed very healthy, low maintenance aquariums/pond.

    It would be great if after a year or two, you updated your instructables with what you would have done differently (if anything) with the hindsight of experience.

    Again, great job, I am really impressed with the concrete work!!


    12 years ago on Step 15

    That is a serious project! i like the pot-waterfall thing, how come in some pictures it is green (which i like) and in other pictures it is plain terracotta? just a different pot?


    Reply 12 years ago on Introduction

    Same pot. The older pictures show the new terracotta pot while it still has the clay color, the green is actually algae growing on the pot over time as explained in step 14: Build and install the fountain, second paragraph last couple of sentences...


    12 years ago on Introduction

    Looks great. The only question I have is how secure is  it from being a drowning hazard to small children? I understand that first they would have to be able to crawl over the pond wall, but kids can be pretty resourceful when the sound of moving water attracts them, and they learn that there are fish to watch, they'll be back for sure.


    12 years ago on Introduction

     How do you keep both the raccoons and the great blue herons from turning your lovely fish into a buffet table?  Everyone I know in our central Ohio area has stories about how their numbers of expensive fish "disappeared"....some without a trace.....(heron) or with minced koi at the edge.(raccoon).  Just wondering.  Sounds like a beautiful project, but in our area....a futile effort.