Moving Koi Indoors: Overwintering Inside

Koi are Poikilothermic (cold-blooded) and have adapted to handle cold temperatures. Their metabolism and overall activity is dependent on the ambient water temperature. As the temperature drops, so does their appetite and movement as they settle into what is essentially a state of hibernation.

As the water starts to cool, it becomes more dense, and at 40ºF it will sink to the bottom and form a warmer zone than the water above it. Koi can use this “oasis” of warmer water to stop from freezing during those cold months of the year.

Constructing a dome or “greenhouse” over an outdoor pond is a good way to trap any residual heat under it and to help maintain higher water temperatures. Some enthusiasts will go as far as to set up a heater under the dome to add to any existing heat. There are other means of helping your koi to weather the winter more effectively, too (which we covered in this blog).

However, there are some koi enthusiasts that just enjoy the company of their koi year round, or who might have invested a significant amount of time (and in some cases, money) on their Living Jewels who won’t leave it up to evolution, Mother Nature or the potential for faulty equipment to decide their koi’s fate. Overwintering their koi indoors and out of the more severe elements then becomes an annual event.

If you are considering bringing your fish inside, here are some factors that might influence your decision to move your koi indoors for the winter as well as some things to consider when you do.

Severe winter temperatures

Cold snaps that drop temperatures below freezing for extended periods can reduce the ability of deicers and aerators to keep holes in the ice for gas exchange. The depth of the outdoor pond and/or if it is an above ground pond will also impact how your pond freezes. Ponds under two and half feet deep are more at risk.

Do you have the space?

Depending on the number of koi that you have (and, more importantly their size) you might not have enough indoor space to house your koi indoors. Here is a general stocking guide to help with choosing the correctly sized container.

How big are your fish?

The bigger your fish, the bigger your indoor tank and higher the volume of water will have to be. Even if you have the same number of total inches of koi, if the majority is taken up by larger koi, you will need a higher water volume to maintain water quality.

They will continue to grow

If you are feeding them throughout the winter, your koi will continue to grow. This is something that you will have to consider when you choose and set up the tank.

Relocation stress

Handling your koi or moving them from one location to another can cause some stress which can in turn heighten the risk of illness in a warmer environment. Transferring water from your pond to your tank can help with the transition.

Similarly, the water temperature shouldn’t be vastly different between the two environments. A container with existing pond water to which indoor tank water is incrementally added will help slowly adjust the koi to the new temperature.

And cover the tank. Koi will jump, and a new environment often seems to make them a little more, well, jumpy while they acclimate. Anchor the cover down, too.

Feeding

Depending on the temperature of your water, you might have to continue your feeding regimen. If you are looking to keep the waste low, consider wheat germ feed in the winter months.

“Seasoning” your indoor filter

Your now-warmer koi’s metabolism will speed up, which means more fish waste in their winter home. This means that your filters will have to be able to accommodate the additional waste and the nitrogen cycle. The beneficial bacteria needed to facilitate breaking down waste will require time to develop. You can season the filter in the summer environment and then transfer it once the koi are relocated as well as add liquid beneficial bacteria boosters.

Indoor holding tank options

Stock tanks or an aquarium are the most popular and readily available options for moving koi indoors. Where you will locate your winter tank will have a bearing on your wintering regimen. A heated garage or basement facility means higher water temperatures, and so will require a different feeding schedule, and more frequent water changes and quality checks.

Some enthusiasts advise against aquaria depending on the size and number of koi, primarily because of the waste management requirements. There is also the aesthetics of viewing your koi from the side versus from above.

Stock tanks come in various sizes and should be chosen according to the minimum requirements for the quantity and size of fish that you’ll be bringing indoors. Bear in mind that galvanized tanks can release zinc into the water over time. A pond liner placed inside can resolve this issue.

Regardless of your decision, we hope that you enjoy your koi this winter and are always ready to help you with your next quality koi purchase. Join our mailing list by entering your email on our homepage and stay up to date on all of the great offers we have on our koi fish for sale.