Keeping Koi in Cold Weather Climates

June FOTM Photo Contest Starts Now! Fish of the Month
🏆 Click to enter! 🏆

10 Tanks

Fish Herder
Apr 11, 2022
Reaction score
Hello Koi Keepers or Would Be Koi Keepers. I have an insulated,, above ground, 300 gallon galvanized steel trough in my back yard and keep Koi and Goldfish in it all year. The inside of the tank is coated, so the galvanization process can't leach zinc into the tank water and potentially poison the fish. For my money, Koi are the hardiest fish you can keep. They'll live in the warmest as well as near freezing water. I keep a trough heater, so the water never freezes. Here in Colorado, some evening temperatures during the winter can fall below zero. If you keep a trough heater going the fish will be fine. A heater will allow you to keep a bit shorter tank too. Mine is roughly two and a half feet deep. The water temperature in the dead of Winter never gets below 50 degrees and on sunny days, which most days are in Colorado, the fish are active and always very hungry. I back off on the feeding in the Winter months. I generally feed half what I feed in nicer weather. A back yard tank, once set up, doesn't take any more care than an inside aquarium. In fact, it takes less. My outdoor tank isn't filtered. It's heavily aerated and gets a large water change a couple of times weekly. Clean, treated tap water is the key to keeping any fish healthy. Go on, get yourself an outdoor tank and customize it to your liking. Then, go out and get some Goldfish or even Koi.

Last edited:
I've stopped keeping koi ever since 2005. But have kept and bred them ever since mid 1980's. I always let the surface freeze during winter (pump and filter weren't running during the winter season). And during the cold period, they started to rest for a couple of months. And such a rest period is good for them as well. In one of my ponds I had a heater but it wasn't needed in order to give those fish their period of rest. My koi did well and grew fast all those years.
Hello. Technically, the Koi aren't mine. I keep them during the Winter months when the local botanical gardens closes their water feature during the Winter. When the nice weather arrives, I transport them back to the gardens in large trash bags. I just acclimate them from one place to the other. These fish are so tolerant of their separate environments. I'm sure my water conditions don't match that of the water feature other than the depth is roughly the same. Their size and colors are really amazing.

I know peoples who have them in their swimming pool during winter, then move them in a large bare bottom tank in their garage during summer, every year.

They fill the media of a strong filter from the swimming pool gunk before switching them to the tank...

And his fishes are looking "Top shape" !!! He just keeps fattening them every seasons, and directly siphon as much poop he can during this time (it's some pencil size stuff) and top off water, Anyway with all that siphoning it's enough for water changes in a week.

I wouldn't be able to spur the required dedication for such a roll over. But still the fishes are on their own nearly 8 months of the year. And are thriving.

I met this guy in a bowling league... You never know.
Hello MaloK. My outdoor tank isn't filtered. I just change out a lot of water every three to five days to keep the dissolved waste out of the tank and I don't feed very much in the Winter. Fortunately, we haven't had the extremely cold nights we typically have this time of year. But, I know you understand cold weather.

Hello. I've heard that as well. But, I believe that would apply to an unheated pond where the water can freeze on the surface. This would make feeding next to impossible. My outdoor tank has a heater, so the water doesn't freeze. I've fed my Goldfish during the Winter for several years and never had a problem. I've been feeding the Koi the same. The water is warm enough that the fishes' metabolism is able to digest a little food. I feed a little three to four times a week. Thanks for the reminder.

Is there anything to the story that you shouldn’t feed outdoor goldfish and koi during the winter months ? I heard they don’t digest food when it’s cold out .
Yes, only when it's that cold, they'll stop eating. Their metabolism will go down.
An interesting thought occurs to me . How long will they go without eating and is it a type of hibernation ?
Actually, when it's cold enough, they will hibernate. They stay at one spot on the bottom to sleep during the cold. During that period they won't eat. Which can be up to 3 months, depending on how the cold lasts, of course.
We're in the middle of a freeze in the uk mine are all huddled together near the bottom they're fine like this every year
Hello. Just checked on my outdoor tank and the fish are swimming around the heater. They'll do that for a while and head for a covered area. Here in Colorado the temperature is in the 40s, but will warm up to the 50s by afternoon. The tank is covered by a pergola, but the water will get direct sunlight several times during the day. I fed all the fish a little pellet food this morning and they seem very active for this time of year.


Most reactions