Koi Pond Guide

A koi pond can be an excellent addition to any landscape. There is nothing more relaxing than sitting back, listening to the bubbling water, and watching your koi fish gracefully swim along. This guide will help give you the knowledge needed to create and maintain your own pond.

First, let’s give you some ideas if you don’t know exactly what type of koi pond you want to build.

Ideas

Typically koi ponds will be one of the two types:

  • Formal – Usually geometrically shaped using straight lines
  • Natural – Look like they were transported directly from nature and into your backyard

Formal Ideas

formal koi pond
Winslowchen, CC BY-SA 3.0, via Wikimedia Commons

Formal designs can have curved designs and be in-ground like the one above.

modern koi pond with patio

You can also include a patio and walkways. Giving the koi pond a modern design.

Above Ground Koi Ponds

The cool thing about a formal design is that you can include seating, and raise it up off the ground. This makes viewing and taking care of the pond easier.

above ground koi pond
Emack2020JPEG, CC BY-SA 3.0, via Wikimedia Commons

Imagine sitting on the bench and hearing the water bubbling into the water from the water spouts and, at the same time, looking over and being able to hand-feed koi fish.

You can you wood to build an above-ground koi pond. But, it must be braced sufficiently and usually still requires you to make the interior pond walls out of cinder block.

Natural Looking Koi Ponds

A well-done natural looking koi pond is hard to beat. The boulders and plants will often add more dimension than a formal design. Bringing everything to life and making you feel like you’re in paradise.

koi pond in kyoto japan
Withlocals B.V., CC BY-SA 4.0, via Wikimedia Commons
japanese koi pond with plants

Notice how the plants soften the edges of the pond. They also add more color and texture.

koi pond with bridge

Bridges are often included in koi ponds and are a great way to get up close to the fish. The above designs allows you to sit on the bridge and dangle your feet into the water.

You will want to locate your koi pond right up close to your patio if you have one. You are making it simple to go out and relax. Please don’t think you should put it in the low area of your rear yard (this is the worst spot as it may flood and can be hard to get to).

Indoor Koi Ponds

Bringing a koi pond indoors solves some issues that can be had with outdoor ponds.

  • There is no need to protect fish from predators like raccoons and birds.
  • Easier to take care of (especially during winter).
  • You can enjoy the pond year-round if you’re in a cold climate.

We would generally recommend a greenhouse attached to your home, not inside it. This will avoid the potential dangers of leaking water, and added humidity.

Here is an example of a fantastic greenhouse with a koi pond attached to a brick home.

Supplies You’ll Need

You would think you could just dig a hole in the ground, pack it down, and fill it with water, right? Unfortunately, it is not that easy, especially when it comes to koi ponds.

As with any living thing, koi fish need the proper habitat to live a good life. And to do that, we have to use the right koi pond supplies.

Liner

Flexible Rubber Pond Liner

installing koi pond liner

There are a few different choices for koi pond liner. In a typical pond, you would use an EPDM rubber liner. The main company that manufactures it is Firestone (website).

EPDM pond liner comes in thicknesses of 45mil and 60mil. Most pond builders use 45mil.

Flexible liners work well if you go in-ground and build a natural-looking pond. Formal ponds with straight walls and 90-degree corners will be better off with other liners.

Concrete Koi Pond Liner

A more permanent and durable way to line a koi pond is to use concrete. Using concrete will be more expensive and take longer to build, but the result will be much better.

Pond contractors will excavate a pond, install plumbing and bottom drains, and layout gridwork and forms. Then, concrete is sprayed and forms the liner. On top of the concrete will usually be some form of polyurea. Think of it as a bed liner for trucks, but only for your pond.

Polyurea will prevent leaks and help the concrete last longer. And look better.

Here is a video that shows the process of how concrete is installed:

Note how they mixed the two designs, formal and natural, using boulders.

After watching the video, if you think, wow, it’s like they are creating a swimming pool! You are correct; koi ponds done right are swimming pools for fish.

Filtration

Koi pond filtration is the next main item that will need to be addressed. The rule of thumb with filtration is you can never really have enough, and more ponds don’t.

Pond-keepers will often get excited and buy many koi fish and goldfish. They are not thinking about the filtration required or that all of those fish can quickly grow to twice their current size. Not to mention breed and create more fish! Which often means the pond filter becomes undersized for the amount of waste produced.

There are quite a few options for filters, and your pond design will dictate what is best.

Here is a brief summary of some common filters:

Koi Pond Skimmers

Skimmers are an essential part of every koi pond. And there are many different products and methods to create a skimmer.

You can purchase a koi pond skimmer from a major manufacturer. They can be pretty costly, but they will benefit you with a quick and easy install.

Or, you can build your own skimmer. The most common DIY koi pond skimmer is the intake bay.

Video showing the standard pond skimmer vs. an intake bay:

In general, an intake bay or homemade pond skimmer will work better and cost less. The main reason being the debris baskets in most pond skimmers are too small and get clogged up quickly. You can make an intake bay or other design as large as possible.

Biological Waterfall Filter

Biological waterfall filters for koi ponds are similar to skimmers; you can buy one or build one. Once again, making one will often be cheaper and more effective.

And the same rule applies, make the filter as large as possible.

One of the best biological pond filters is called a “wetland” or “bog” filter.

Aquascape Inc. Wetland Filter System

It is essentially just taking the water being pumed from the skimmer and bringint it to the bottom of a bed of gravel and small boulders.

The stones create surface area for beneficial bacteria to grow and process nutrients.

The bog filter also allows the use of plants. Aquatic plants such as reeds can be planted in the bog filter, and the roots will also take in nutrients and help filter the pond.

The Aquascape Wetland filter system is a fantastic ready-made kit for this filter. Although, if they are out of your budget, it is possible to build your own (IPPCA website) using sewer pipe.

Backflushing

Whether you build a waterfall filter or buy one, a feature to include is the ability to backflush. This will help keep debris from building up in the filter, allowing the filter to function optimally.

UV Lights

UV lights for koi ponds are great for springtime in cold climates as they will assist the primary filters while the water is cold and the bacteria hasn’t fully kicked in yet.

If you see green-colored pond water, UV lighting can help.

Pump/s

A koi pond pump is what keeps everything alive. Think of it as a human’s heart. Pumping blood and oxygen, but obviously water and oxygen in the case of a koi pond.

Two things about koi pond pumps are:

  • Make sure they are sized correctly (the minimum flow rate should circulate the entire volume of water once per hour).
  • Have a backup pump if air pumps are not used in case of power outages or a pump failure.

While traditional water gardens typically use submersible pond pumps. Koi ponds often use external pumps. There are outside of the pond skimmer.

This PDF of EasyPro external pumps will get you more familiar with them if they are new to you.

External pond pumps will usually last longer than submersible pumps and are more energy-efficient.

Plants

aquatic pond plants

Aquatic Plants

To make your pond look and function better, you should add aquatic pond plants (website). They will improve your water quality, and your koi fish will thank you.

There are four main types of koi pond plants:

  • Floating – Float on top of the water surface and dangle into pond
  • Bog – Often best in gravel waterfall filters
  • Marginal – Used on the sides of the pond in shallow water
  • Emergent – Grow and bloom from below to above the water surface
  • Submerged – These plants provide cover for fish, a place for eggs to hatch, and oxygen

Surrounding Landscape Plants

The area around your pond will also greatly benefit from plants. The most common plants are Japanese maples and evergreens. As since koi fish and ponds were first developed in Japan, that is where most of the designs are influenced.

Just make sure that what you plant does not drop a large amount of debris into the pond water, as this will cause excess nutrients to build up—leading to pond algae. Not to mention more maintenance of cleaning out a skimmer debris basket.

Maintenance

Koi pond maintenance can be just like cutting the grass. Something that is required regularly but isn’t that bad. Unless, like grass, you neglect it for too long.

Common maintenance tasks include:

  • Backflushing waterfall filter
  • Emptying pond skimmer debris
  • Using a skimmer net to get any debris that was allowed to sink to the pond bottom
  • Planting, trimming or removing pond plants
  • Monitoring water quality and level
  • Adding water treatments such as barley straw extract or beneficial bacteria
  • Feeding fish and handling any issues that come up fish related

Winter

Maintaining a koi pond in winter is not that difficult. You just need to keep a hole open on the surface for proper gas exchange. This is usually done with a pond-deicer. A small saucer that uses electricity to keep a small area around it open.

You will also want to include a source of oxygen. Often the main pond pump gets shut down, and you add a small air pump with an air stone on the bottom of the pond.

Your koi fish will then hang out in the deepest part of the pond and wait until springtime rolls around.

You will want to keep an eye on water levels through winter. Sometimes, ice buildup can cause the water level to fall too low.

FAQ’s

How deep should a pond be for koi?

On average a koi pond should be 5-6′ deep.

How expensive is a koi pond?

A koi pond can cost as little as $500 or up to $1,000,000 (yes, there are that expensive koi ponds). The average we estimate to be $5,000 – $10,000. Depending on how much the homeowner does. A professional contractor will often cost $15,000 to $30,000.

Are koi ponds high maintenance?

Again, this comes down to the design and size of the pond. On average, plan on 15 mins a day minimum. This includes emptying skimmer debris, feeding fish, and checking water levels and filters.

How often should you change the water in a koi pond?

Great question. Water changes are a regular part of a healthy koi pond. We suggest 10 – 20% per week be changed. You can often make this automatic by slowly filling the pond with an auto-fill and allowing the water to trickle out of the overflow.

How big of a pond do you need for koi?

At a minimum, your pond should be 8′ x 10′ and 5 feet deep. But, bigger is better.

Do koi reproduce in a pond?

Yes, koi can and do reproduce in ponds.

Can koi fish bite?

Well, by bite, assuming you mean with teeth. While koi fish do have teeth, they are located in the rear of their throats- and are flat shaped for grinding food. Not sharp canines. So no worries about being bitten by koi.