How to Construct an Indoor Koi Tank

How to Construct an Indoor Koi Tank

If you have done your research, you are probably well aware that keeping koi long term in a traditional fish tank is not the best idea. 

Koi are large, beautiful fish who require a lot of space to move about. 

They can get over three feet in length and live more than fifty years! 

These fish are truly a commitment. If you still want an indoor enclosure, let’s discuss the steps you can take to build a suitable indoor koi tank!

Why House Koi Fish in An Indoor Koi Tank?

As you probably know, koi are typically housed in outdoor ponds

They do well in large ponds with a lot of space, shade, and food. 

These stunning fish are a great dynamic accent to any yard and offer such a rewarding care regimen that is simple yet gratifying. 

You get to literally see these beautiful animals in an environment where they are comfortable and thriving.


Still, for some people, outdoor housing may not be an option. 

Predators can prey on koi and if you live near a lot of wild animals and birds, you may not want to keep them outside where they can become a meal for a forest creature. 

Those who live near farms or other areas that may use chemical pesticides or other treatments also may not want to keep koi outdoors either since these chemicals can make the koi quite sick or even kill them.


Temperature and just preference can also play into deciding to keep koi indoors. 

Regardless, though it is a less popular option, you can keep koi happy and healthy inside of your home if you opt to steer clear of store tanks for larger fish, especially if your plan is to just have them inside for the winter or other set time periods.

Building an Indoor Koi Tank

When creating an indoor koi tank, it is important to mimic the same conditions your koi would have outside. 

Due to this, many people recommend using a similar method to constructing an outdoor pond. 

There are many different methods available, all of which are viable in their own right. 

You should research and figure out what best suits your needs. 

The idea we have below is for example purposes only and to offer you an idea of what to expect as a normal plan to build a pond.


For starters, you will want to ensure your setup is structurally sound and able to support quite a bit of weight from the water and movement from the fish. 

Due to this, you need to invest in either a high quality, pre-built base or have one built. 

Typically these are constructed of metal or wood.


Once you have a base, you can then begin the process of creating the layout for the water space. 

To do this, you can use sheets of fiber, waterproof plastic, or another material that can be laid flat to form the “bowl” of the tank. 

Coat this in several coats of pond sealant or liquid rubber to further waterproof the tank.


It is important to remember that you must incorporate portholes for filtration, heat, and other tubing that you may need. 

Be sure to include this in your design and do not cover these areas with the sealant, as you will have to remove it and relay if the guide holes are covered.


A lot of people also recommend sealing down the edges of the pond before adding the sealant to give it a more smooth finish and prevent the overlay from pulling away from the sides over time or developing bubbles.


We recommend you look up specific plans online and use them as a template for your own tank. 

These are delicate proceedings so if you are unsure, it is best to hire someone to create a piece that will suit your space and volume of fish perfectly.

Preventing New Tank Syndrome

Used to refer to the stress and illness that can come from adding fish into an uncycled tank, new tank syndrome can be fatal, especially if you add a lot of koi at once. 

It is recommended that you allow the new tank to filter for at least two months before you bring your fish into the new space. 

This process allows your pond to properly develop good bacteria and sort out a balanced nitrogen cycle before you add in the fish who rely on these factors to survive.

Additionally, you can use this time to check for any defects in the formation of your tank. 

Leaks will be easier to fix without having to move fish around and other issues can be remedied before the animals are ever added. 

This makes maintaining your tank easy and prevents injuries or mishaps down the road since you have a bit of a fish-free trial period to work out any kinks.

Build Your Indoor Koi Tank Without Cutting Corners

When building your tank or having it built, do not cut corners. 

The last thing you want is to have the tank suddenly rupture and spill hundreds of gallons of water out into your home, injuring your fish in the process. 

Invest in good quality tools and mediums and always check and double check sealants and other protective areas of the pond for leaks and other malfunctions.

Your indoor pond/tank will act as a unique, controlled ecosystem. 

It is vital to the success of the enclosure that you maintain and double check everything you can to ensure nothing goes wrong. 

Your fish will be happier and healthier with these precautions!

Creating AN Indoor Koi Tank: It's A Process

Creating an indoor koi tank from scratch can be a rather intensive process but if you are looking to become a serious koi keeper, it is worth the time and investment of money.

Koi are very rewarding animals to keep as pets and deserve all of the space and add ons they require.

Do not be afraid to reach out for help and always err on the side of caution.

It is better to be too protective than have to remedy a situation later. Good luck!