Building Your Koi Pond: Learn the Basics to Get Started

Section 1 – Choosing the location

One of the biggest challenges in constructing a Koi pond is finding the right location for it.

Having a koi pond that is either inaccessible or hidden defeats to the reason why you installed a Koi pond in the first place!

Here are some points you should consider when planning your koi pond installation:

1.)  Accessibility – you wouldn’t want your pond to be inaccessible and away from people. One of the great things about keeping a koi pond is it immediately brings delight to the people who see it. Having to go through several obstacles just to see your fish isn’t going to be convenient to guests that want to check out your pond.

2.) Visibility – the view of your pond should be largely unobstructed. One thing many folks do is plan for a dedicated viewing area.

3.) Cohesiveness – your pond should blend in perfectly with its surroundings, not stand out or be swallowed up by it. Your pond should look like part of the landscape. As a word of caution, be aware that shade is good for your pond and fish but putting your pond near/under trees will result in falling leaves into your pond that will decay and cause water quality issues.

One way to effectively visualize your pond for appropriate fit into your surroundings is to mark out the spot where you’re going to put it with spray paint. A bright orange spray should make it stand out so you can view it from different angles. Other folks will lay down string or garden hose to map out the pond.

Once you’re satisfied with the location of your pond it is the right time to start digging. Give it a couple of days or so before you pick up the shovel just to make sure you are 100% happy with the location.

Section 2 – Size and depth matter

Once you’ve decided where to build your pond, the next thing you need to do is determine how deep it will be.

Not surprisingly, you will need a larger pond for a greater number of fish but you will also want to plan for the increasing size of fish through the years.

For the average koi pond keeper, a pond 24 feet long by 12 feet wide with a depth of 4 feet should be sufficient for mid-sized koi. This depth will also allow for pond freezing in winter. This volume should be enough to accommodate ten 24 inch fish or twenty 12 inch fish without overcrowding issues. Another good rule of thumb for both aquarists and pond keepers is “less is more”.  More fish in a pond won’t necessarily bring you more happiness. In fact, more fish can sometimes translate into more maintenance and issues.

In order to calculate the volume of the pond you are wanting to build, use this formula:

Length (of the pond) x Width (of the pond) x Depth x 7.5 = Volume of water (in gallons)

or see this online calculator.

Section 3 – Everything falls to the bottom

Since your new koi pond is occupying a large space on your property, things are eventually going to fall into it. Leaves, dirt and other debris are going to find their way into your pond. And that doesn’t take into account all the fish food and droppings that are eventually going to find their way to the bottom of the pond.

This is where the bottom drain comes in.

Bottom drains in koi ponds are pretty standard and a four inch pipe leading out is optimal. Organic matter that falls to the bottom will eventually become pond muck. It will build up and make your pond stink which defeats the purpose of having a koi pond.

A bottom drain effectively sucks this all up, sends it into the filtration system for proper filtering, and disposes of it. The bottom drain is your first line of defense for muck build up.   The “old school” mode of thinking was to simply have a gravel lined pond bottom which, on the one hand is good because it allows for lots of surface area for beneficial (nitrifying) bacteria but on the other hand it allowed lots of muck to accumulate.   This resulted in the necessity for regular yearly (usually spring time) cleanings of the pond which involved draining the pond and removing all that slop. Very messy! The bottom drain will drastically reduce the amount of muck removal and cleaning you will have to do.

bottom-drain for koi pond
Typical bottom drain

Tip: Be sure that your pond is not too close to trees as leaves are bound to end up in your pond and will not only be unsightly but can decay and throw off the chemical balance of your pond.

Section 4 – The Filter System

Achieving clean water is ensuring good koi health. For a koi, the pond is their entire world. That means they breathe in it, sleep in it, feed in it and eventually pass their wastes in. If you don’t have a pond equipped to handle the wastes, it could become very dirty in a short period of time and you’re going to end up with very sick and unhappy fish.

You need a proper filtration system to avoid this.

There are four essential components of a koi pond filtration system.

Bottom drain – we’ve already covered this in the previous section so you are already familiar with the function of this and why it is essential to your pond’s success. A 6000 gallon pond can function properly with just one bottom drain. A larger pond will mean installing another bottom drain to effectively clean your pond’s bottom (benthic) surface.

bottom drain and cross section

Settling chambers – the bottom drain typically dumps out at the settling chamber.  As the name implies, this is where heavier solids settle out and the pump then pulls water out of the top of the settling chamber, which then passes through mechanical and biological filtration and back to the pond.

settlement chamber
Settlement chamber

Mechanical filtration equipment – this is what filters out the bulk of the debris. This happens as particles are trapped in the brushes of the equipment. Since this will eventually get clogged you must make sure you buy the equipment that ensures you will always have replacement parts or brushes when it is time to replace them.   Mechanical filtration is usually set up in stages where coarse mesh material catches larger debris first then subsequent filters are finer mesh and sieve out smaller debris.

Biological filtration – this is the chemical portion of the filtration process. Ammonia and nitrites are ever-present in bodies of water where fish live. These are the products of their waste which need to be processed in order to make the water habitable. Your pond performs this biological filtration on its own to a certain degree but having dedicated filter media where beneficial bacteria can thrive and perform the important work of assimilating the harmful ammonia, nitrites and nitrates is crucial to the longevity of your pond.

As soon as everything is broken down, the processed water will go back into your pond, much healthier than it started. Testing for ammonia and nitrites should also be done on a regular basis to ensure that everything is functioning well and that your biological filtration is in good shape.

Tip: Some pond owners are confounded by sudden increases in nutrients -this can often happen after a rain storm to ponds that are near places like golf courses or farmland.

book on how to build koi pond

Got questions? This book is a great reference to have around both for planning a koi pond and while you’re still waist-deep in a hole trying to figure things out.

Section 5 – Time to bring out the shovels

 There are three primary ways to install a pond.

• Prefabricated mold (plastic or fiberglass)

This is the most expensive option but what you save is hassle. This system only requires that a hole be dug that matches the mold’s shape.

• Liner (vinyl or butyl)

This is probably the most cost efficient manner of creating a pond and probably the most popular method used by koi owners all over the world. It allows for a lot of customizing and you can really use your imagination with this material. What you save in cost is countered by the greater effort to install.

• Concrete

This is the most expensive manner of fabricating a pond but also the one that provides a lot of flexibility in terms of creating a pond matching your expectations. Though more expensive than the previously-mentioned methods it offers substantial strength and leak-proofing.   Another added benefit is that is helps to buffer swings in pH due to the carbonate in concrete and grout.

It helps to set out all of your materials so you know where your equipment is going to go when the pond is complete. Measure each piece so you know the actual dimensions and determine just how far you should dig. In the following example a pond is being built using a vinyl liner.

Excavate the entire area within your outline to about 9 inches deep. This should effectively set your pool area apart from the rest of the area and give you a better visualization of what it will look like in the end. Avoiding a perfect circle shape for your pond will help steer clear of the “necklace effect” which results in a “necklace” of rocks lining the pond edge. A better shape to shoot for is essentially an irregular shape that allows your pond to look more natural.

The next thing you should do is dig a trench along the outline you traced on the ground. A trench about 12 inches wide and 12 inches deep should be sufficient. This is going to be your initial shelf where your ornamental rocks will be positioned.

Place flat wooden stakes all around the diameter of the trench’s sides. This means both sides so you’ll have wooden stakes on the outer layer and the inner layer. This is where you are going to place your plastic shaper so that the cement you pour in is going to conform to the shape of the trench.

Before pouring the cement in, place some rebar to create a basic framework or support system for the concrete once it hardens. This will also allow the cement to retain its shape once this process is done. Tie the ends of the rebar together with some wire and then elevate them with a small block of cement as evenly as you can all throughout the diameter of the trench.

Now pour the cement in. Make sure that the volume of cement per feet inside the trench is consistent. After that, use a wooden planer to level out the top of your cement.

Allow for the cement to harden before moving on to the next step which is to remove the plastic shapers and continue digging out the hole. The cement should be ready after letting it sit for about 24 hours.

After that process is done, you can excavate the area interior to the concrete. With the cement bench in place, you should be able to excavate as vertically straight as possible along the edges.

With respect to depth, a good depth should be around 4 to 5 feet. It’s deep enough for the fish to have some variety in terms of swimming depths, thermal refuge during winter and shallow enough for the average person to get into to provide preventive maintenance care on a regular basis.

Make sure the bottom of your pool has a gradual slope towards the center of your pond. This is where you’ll be installing your bottom drain. Another thing to note is that if you live in an area cold enough to cause your pond to freeze over you will want to angle the sides of your pond in (towards the pond center) around 15 degrees to allow for the expansion of ice to slide along the angle and not outward against the liner.

The next step is install the bottom drain and anchor it at the lowest part of your pond. You will need to dig a deeper hole to set the foundation of the bottom drain and a trench for its pipes to run through. And then you will have to anchor it down so there is no unwanted movement which could compromise the fittings of the pipes. This movement is usually caused by water pressure from all the water movement.

The next thing you need to make sure of is that you have the proper returns and fittings installed for the pump and filtration system. One great thing about the filtration system is that you can elevate it and hide it with some strategically placed rocks to emulate a waterfall. This should help you create a waterfall effect. Your returns on the other hand can be placed in several locations to create several vortices to direct the water flow.

Another important addition for your pond is a skimmer to keep the surface of your water looking great and to keep floating debris like leaves from ever making it to the bottom to decay.

skimmer box
Skimmer Box

Whether you have a sunken pond or a raised fish enclosure, it’s always best to keep your liner and plumbing hidden from view. Nothing is more unsightly than exposed plumbing and liners. But there’s another reason why you should hide these from view. Since your pond is essentially going to be an outdoor fixture, it is going to be exposed to the elements. Your liner and plumbing which is made of a plastic and vinyl mixture is eventually going to be damaged over time and either crack or warp.

Remember the shelf you made with the cement? This is where your liner will rest being held in place with rocks over the edges. Do not cut the edges of your liner until you are absolutely sure that everything is set and in place. You will want to lay down a layer of sand or something that will help cushion the liner from possible puncture prior to setting in the liner.

Another thing to be aware of is to ensure that the edge of your pond is slightly higher than the surrounding areas to prevent rainwater from flowing into the pond. An elevation of an inch or two should suffice unless you live in an area that gets plenty of rainfall. 

Basic Pond Construction with Liner

Final Thoughts

The methods and techniques presented here are typical and used successfully by many however it should be noted that there are LOTS of ways to build a healthy pond. There’s lots of ways to filter water and not just one, tried and true method. For example, some folks don’t have bottom drains, some folks would never consider using a liner while others swear by it. Your particular situation and finances will dictate what kind of pond you install and the size of your filtration you need.   Beyond the foundation of your pond, the components you want to put the most energy and investment into is your pump and filtration because those are your heart and kidney’s of the pond.

8 thoughts on “Building Your Koi Pond: Learn the Basics to Get Started”

  1. I don’t have a bottom drain in my pond which is about 12′ x 8′ x 5′. I have a three level waterfall that goes into this bottom pond that was recently redone. I had gravel in the bottom pond that was removed on advice given me by a koi expert. When the waterfall was redone, the company removed our 3′ x 3′ lava rocks which we had in our previous top waterfall. They replaced our filter with a new slighter larger in ground skimmer and 9″ weir but took out the brushes that were in it because it impeded the water flow. They only left in the media filter inside the box. We now have no biological filter but do have a UV light and oxygen stone in the pond. We had nine koi for eight years with no problems and now have lost all but two to disease and bacterial infections. Do you have any recommendations? Should I replace the gravel on the bottom of the pond? We have a liner and not concrete. I was thinking of possibly putting in a bog filtration.

    • Hi, so one of the things that the gravel did in your previous situation was to provide surface area for beneficial bacteria to colonize and subsequently assimilate ammonia, nitrites etc. however despite that benefit it makes it really difficult to clean the mulm from the bottom of a pond especially when you don’t have a bottom drain. So I would agree with the advice you received about removing the gravel but you will need to address the issue of biological filtration which you are short on now. You will really want to look into a biological filter that is easy to clean and has tons of surface area (media like bio-balls) or, as you mentioned, you could do a bog system above the pond. If everything is going like it should its a nice system to have but not everyone has that option. UV is good but it needs to be cleaned if you don’t have a wiper on it and will need replacement every year or so (just make sure its appropriate for the volume of water you have and the flow rate is not too fast going by the light). Air stones are always a good addition to any pond. You have a liner but I believe with some effort you can retro-fit a bottom drain in that pond if you want to go that route. Bottom drains are really nice to have -its kind of like indoor plumbing in a house -really nice to have but you could also have an outhouse….
      So you have some options here. Bog filtration would be great but the quicker solution is going to be a filter with lots of surface area for beneficial bacteria growth. You could also retro-fit your pond with a bottom drain and save yourself the effort of vacuuming and save yourself the buildup of muck with can add to disease issues. 90 percent of people that contact me about koi issues are related in some way to water quality which is, of course, linked to their ability to filter the water (and there’s lots of ways to do that). I do carry some filters on my store but there’s lot of options out there. If have the motivation to do it a bog filtration system would be great to have.

  2. I do not have a pond. Always wanted a pond, but am having a hard time understanding, do I need a filter, pre-filter, skimmer, bottom drain, etc. The list goes on and on.
    Are there any simple “how to” books that are for the beginner. For what works and does not work without going through trail and error.
    I have a liner, skimmer/pump box, place to put the pond, but need a kick start to get going.


    • John, it can certainly be confusing if you are just starting out. One book I recommend is this. Doesn’t cost much and you can always get your money back if it doesn’t answer your questions about building a pond. This book takes a certain approach but there are lots of ways to look at it and opinions will differ however most pond keepers agree that a bottom drain is, although not critical, is really important (sort of like saying that one does not necessarily need indoor plumbing, but it is sure nice to have!). From years of keeping fish I would suggest that less is more. Some pics you will see of koi ponds show the surface covered in koi but a dense koi population can also introduce more problems and headaches. The koi will enjoy life more if the pond is not crowded and you will have less filtration issues because of it. You have a liner -thats good but that means you will have to account for KH (the potential for pH to swing). One way to mitigate for pH variations is to have a concrete constructed pond which isn’t an option for you however there are simple solutions for liner ponds such as putting a cinder block in the pond or some form of calcium carbonate material. There is also the matter of aeration. Its important and there are better ways to approach it. Some folks like to have a water feature like a waterfall or geyser. Those are fine but the degree of aeration is more limited as compared to air pumps and air stones that inject air into the pond from the bottom rather than from the top which limits water agitation (and thus aeration) to the top layer of water. In the end, you are going to want to piece things together from the book I recommended (or whatever book you decide on) and websites like mine and others. I think its important to get different perspectives on every aspect of having and maintaining a koi pond -it takes a village, after all!

  3. Pingback: Quora
  4. I have a 1200 gallon Koi pond with no bottom drain. I have a pump at the bottom with a hose running up into a waterfall. Needless to say I,m having a lot of murky water. How do I add a retrofit bottom drain? will I need a second pump and filter? I want to correct this and do it right this time. Thanks for your help.

    • So the difficulty of this will largely depend on the construction of your pond; dirt vs. concrete. If its dirt draining will be necessary and then you can retrofit your bottom drain which should lead to a settlement chamber on its way to the pump and filter.

      Similarly with concrete ponds you can do a retrofit but it may have to lay on top of the substrate.

      They ARE a big help though, thats why i stress the installation of them when anyone is considering building a pond.

  5. Hello do you know how will you calculate the return of the water from filter to the pond base on its volume?
    What type of water pump you will use?
    And other stuff that needs to calculate for a proper koi pond …
    Now adays koi keeper is advance and never stop learning and discovering news things on how to improve their individual pond..
    I would love to know more about that stuff.


Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.