Even though it is already winter, and we recommend not disturbing your fish while they are “hibernating”, it’s not too early to start planning for next winter. This is especially true if you are thinking of bringing your fish inside next year.

There are a few things to consider first:

This will likely require different equipment from your pond outside.
The place where you keep your Koi inside will not look like the fancy picture above unless you put a lot of time, effort and especially money into the project. Even then, installing this kind of thing will probably take some time to do as well. So if this is your first time keeping Koi inside during the winter, keep in mind that your set up will probably not look very pretty at the beginning.
It is more time consuming to care for your Koi if they are brought inside over the winter. This is because without the change in temperature, the Koi fish will not enter the state of “hibernation”, meaning that they will need to be continuously fed and continue to produce waste at the same rate that they do during Summer time.
This also means that it will be necessary to do water changes, especially because there is not an unlimited supply of fresh air to combat the gases that are naturally released. It is important to make sure you have a system in place before your Koi are inside, because moving from the pond outside to the indoor tank will likely cause stress for the Koi and they will need their water changed sooner than later.

Ok, now you have either realized that keeping Koi inside during the winter isn’t for you, or you are still in love with the idea of being able to see your Koi year-round. Here is what you need to do:

If you are planning ahead enough, you should be able to set up the tank and all the equipment in your pond outside, before you need it. This ensures that everything is working properly and both your indoor and outdoor systems have the same “ecosystems” (bacteria, etc.).
When the time comes, move your tank set up to your spot inside and make sure to fill it with water directly from your pond. Similar to the reason above, this will make the adjustment easier on your Koi.
Once the pond is filled, it’s time to start moving the fish. The easiest way in my experience to do this is to drain the pond to a level that the fish can still swim easily, but at a level that you can see all the fish to make sure you get them all. If you just(e a net over the opening to make sure that no fish could jump out.
For the first couple weeks, feed only a little bit to avoid excess ammonia levels and make sure to add in a beneficial bacteria to help make sure the ecosystem in the tank is working the way it should.
Once a week, make sure you are testing your water with a test kit (pH, ammonia and nitrite) and do a water change. This is different from just adding new water to the tank. Make sure to take water out of the pond and replace it with new water (and Dechlorinator of course!)

Now you can enjoy your koi year-round!