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.
This is alaa aljuboori live in spring field -MA-USA-01104
I try to buy koi fish small size ,the question is how can you deliver fish to me with good condition
thanks
Hello. We take great care to ensure the safety of fish during all seasons. We have been selling and shipping fish for 10 years, and you should have no worry that your fish will be in anything less than good condition. Thanks.
I have 8 koi fish that are approximately 12″ in length. Every year I bring them in the basement of my house for the winter as I live in Pennsylvania and my pond is not deep enough (approx. 30″). I have 1000 gallon tank in the basement built and I was wondering if I should have a UV light in there to imitate natural sunlight. Any thoughts?
It would certainly not hurt to bring a UV light in to simulate natural sunlight, but I believe that your koi would be just fine without it.
I have one 12″ Koi and two 5″ goldfish that I keep in my small outdoor pond. My pond is about 3 feet deep and I have left them outdoors for the last 3 years and they have been fine, however our last 3 winters have been mild. I live in N.J. and we are never quite sure how the winter is going to be. I am worried about the possibility of a harsh winter and losing my koi. Can I bring him in and keep him safely in a 30 gallon tank? or is that to small?
Greg
No, 30 gallons would not be sufficient to overwinter a Koi of that size.
We want to put a Koi pond in our backyard, but so worried about the winter time we are in Ontario, Canada and we can get some pretty cold winters. any tips that might help?
Hello – I live in MA. I have a 1,000 gallon pond with 8 adult koi and 3 baby koi (at least 5 months old) The largest koi is 8-10 inches long. I want to bring them inside for the winter, but don’t want to stress them out. What size tank would you recommend? Would adding a heater to the pond be a better option? If so, do you have a recommendation for winterizing the pond?
The general rule of thumb is one inch of fish for every ten gallons of water, but you can get away with more if you have proper filtration, aeration, etc. Adding a heater to the pond will depend on pond construction and how much in extra utilities you are willing to accept, among other things. Here’s an article on winterizing your pond – https://nextdaykoi.com/koi-how-tos/winterizing-your-outdoor-koi-fish-pond/
We have a pond outside that is about 1400 gallons in size. There are about 30 koi in there about 5″ long as well as a filter system.. I was thinking about bringing them into my garage for the winter. I have an acryllic bathtub that measures 32″ X 60″ X 19″ high. I was going to put the fish inside and have a small water pump in the water to keep the water circulating, and also not feed the fish over the winter. Would this be OK? Would there be fish waste to deal with and have to change the water at different times? Also, I used to leave the fish in the big pond all winter with a small heater about the size of a frisbee in the water which allowed the transfer of gasses. (The big pond is 4 ‘ deep.). Perhaps I should put the heater in the tub in the garage?? The garage temperature does not get below 32* F or 0* C during the winter. What do you suggest? Thank you.
Thanks for shopping with us. Yes, you can move the koi indoors for the winter provided you are set up to care for them there, which it sounds as though you are. You will still likely need to feed them through the Winter though, as koi feed from the bottom of the pond during this time of year, and in a clean system with water changes often there would be little to consume. If the heater you mentioned is capable of keeping the koi warmer then by all means bring it indoors. Keeping koi warm through the Winter ensures there survival, so if you are able to warm things up then we recommend it.
I have a good size Koi pond and there is a good chance we will be moving this fall. Its just two miles away but the house we are moving to does not have a pond built yet and I doubt I will be able to get one in before winter. I was thinking up setting up a temp holding in the unheated garage, of course keeping the water circulation and not allowing freeze over. The question how big would I need to go. I have 1 around 14 inches 4 around 8 inches and 14 that are between 4 and 6 inches
Hi Nicholas,
It is definitely a good idea to bring them inside in the garage like you plan to do. As far as for the size of tank or set up you will need to house these various size fish, we have attached for a link to another article that breaks down the appropriate size needed to house them.
https://nextdaykoi.com/koi-fish-facts/keeping-koi-aquarium/
Thank you.
Is it safe to give Koi away during the winter months? Is it safe to take them from there current pond when they are all on the bottom and put them into containers and move them to another pond? what problems will this cause for the fish, am i asking for trouble?
Koi can be added at any time of the year as long as you take some precautions, such as proper acclimation. However, we do recommend quarantining new arrivals, regardless of the source, prior to adding them to the community pond. In this particular case, we might recommend not moving them from “hibernation” until the warmer months when they naturally acclimate back to normal. This will prevent further unwanted stress on the fish.
For next winter I would like to put my 2 Koi- about 16″ long now, and 3 goldfish– from 8″-10″ now, in our basement. It’s about 55 degrees down there. Can they go without a heater or filter? As long as there is a bubbler?
Hi Judy, In this case you don’t necessarily need to have a heater. However, it is highly advised to provide filtration. This will ensure that the water is being filtered and cleaned, but more importantly, ample oxygen is being provided to the fish in this temporary set up.
I’ve been taking care of an Injured koi, he should be ready to go back to the pond in two weeks, but it will be December snd he’s been in my basement since September. Will he be ok to place back into the pond or should I over winter him in my basement
Hi Dana,
While you likely could add this fish back to your pond if carefully acclimated, it may be safer to overwinter in its quarantine setup and try re-introducing back in the spring time.