What Is The Best Temperature For Koi Fish?

Temperatures in the 60's to low 80's seems to be the best range for koi
Image by Ilona Ilyés from Pixabay

Summer is in full swing this time of year. Your koi are probably enjoying the sunlight as it trickles down on their scales. Is your temperature actually helping or hurting your koi?

What Is The Best Temperature For Koi Fish? Temperatures in the 60s to low 80s seems to be the best range of temperature to keep your Koi fish in. I’m referring to the water temp here.  If you go lower than that then you will find a pond heater to be very useful. Temperatures 85 degrees and above and they don’t seem to grow as well either. Somewhere between 68-74 is believed to be the ideal range.

What Is The Best Temperature For Koi Fish?

One person who actually grows Koi for shows says that he never lets his water temp get below 64. Don’t ask me how he came to that number but it works for him. Any temperature that doesn’t let bacteria grow unchecked and gets adequate oxygen pumping through your water works well for a Koi pond.

Heat your pond up with a pond heater in the Fall and Winter. Choosing the right pond heater is a very important decision. You need to consider the size of your pond and the weather conditions that you live in. There are three different types of koi pond heaters and have different uses. They are:

  • De-icers
  • Gas-Fired Boilers with Heat Exchangers
  • Inline Electric Water Heaters

Why Does The Temperature Affect Koi?

When the temperature gets down to the 50s then the Koi can’t break down food. Koi don’t have a stomach and their metabolism shuts down at temperatures below 50. That’s why it’s not recommended to feed Koi in the winter. The food will just sit in there and rot causing eventual death.

The good thing about colder temps is not much bacteria is allowed to flourish. This keeps disease at bay and keeps maintenance down. However, oxygen levels also get really low and once you reach around 28° oxygen can no longer be dissolved in the water which becomes the more significant risk factor.

Temperatures of 85° and above can also have an impact on your Koi’s growth and health. Pathogens and bacteria increase when temperatures start to rise. A good reason for a filter. The oxygen saturation in the water also starts declining in these temperatures.

Who Wants To Know How To Keep A Healthy Koi Pond Temperature?

Hopefully, you do if you want non-dead fish. You can go to purchase a pond heater at many pet stores or online to use in the colder winter months. These gadgets will help you maintain a constant temperature year-round. You might not need it on if you live in the states during summer. 

Fall and winter times are a different story. You might need an extra heater or two depending on the size of your pond. Another option is you can also have a pond heater and a floating de-icer. A de-icer shouldn’t be used alone but would be a good addition to your Koi pond heater in a pond 500 gallons or so.

The Functions of Pond Heaters

Dei-icers float atop the water and keep an opening in the water during the cold months to keep gases from building up in under the ice. It allows your pond water to “breathe”. 

Gas-Fired Boilers have a heating system built in that draws your water in, heats it, and then circulates it back into your pond through a heat exchanger. These are excellent for Koi ponds because they work fast.

Inline Electric Water Heaters uses an electric element to heat your water instead of a gas one like the one above. As the water goes through the heating system it is warmed slightly and is then recirculated back into the pond. Keeping this process going results in the water warming up eventually.

Where Do Koi Thrive Best?

Unless you live in the Arctic or the Sahara you probably have fine conditions for Koi to live in. They are a surprisingly hearty fish as well as being easy on the eyes. Some areas, where it is 40s year-round, aren’t good for them nor is the desert. If your area doesn’t fit those two extremes then you have a good habitat for Koi fish to live long and prosper.

Koi are found in ponds all around the world. You see them in tanks in Chinese restaurants. Here in Arkansas where I live there is a place that sells them in Bentonville. The way that they can thrive in so many different situations is what I believe makes them so popular. 

They love the summertime the most. They like the weather and, even more, the moths and insects flying around that they can catch. Koi are omnivorous so the vegetation and lifeforms that are abundant make them fat and happy.

If your pond gets too hot it can also damper your Koi’s health. This is where proper planning of the location of your pond comes in. I would suggest building your pond under a tree or have something that gives off artificial shade. Adding in pond aeration will also help keep your water cool and normalize oxygen levels.

When You Need To Be Concerned

If your fish are popping up for air then there is a concern that there isn’t enough oxygen getting dissolved in the water or there are excess gases like hydrogen sulfide and carbon dioxide. This might happen if you are using a de-icer for making a hole but isn’t big enough.

Don't let the water get too warm for your koi either
Image by marina888lyakun from Pixabay

Try to make the hole bigger using a hose or have another de-icer. This is really why you shouldn’t depend on a de-icer alone anyway. They might not allow enough gas to escape so your Koi are slowly suffocating. Having the gas or electric-powered heater is preferred and then, if you want, you can add the de-icer.

Besides that, don’t let the ice bother you. Like bears, Koi tend to hibernate in the winter, as long as there is a large enough hole in the ice to allow gas to escape they are good. The ice acts as a barrier between the cold air above and the water below and they just sleep away. Just don’t let it get in the single digits.

You’re Fish Are Going To Be Cozy

When you keep your Koi pond at the right temperature your fish will be as snug as a bug in a rug. Don’t let your water dip below 40 degrees so water can still absorb oxygen. The gas-fired boiler heater pump is the best pond heater type in my opinion for maintaining a warm temperature all year long. A de-icer might work for a smaller pond as long as you keep an eye on it.

Water that is too cold can obviously ice over and that can cause problems. This ice can trap deadly gases under the ice and be lethal to fish and other organisms living down under. Keeping your water circulating with a pond pump and using a heating system will alleviate this problem.

What’s wrong with water being too warm in a koi pond? Water that is too warm can cause oxygen not to saturate properly in the water and can cause problems with your fish too. Bacteria and algae can take over further deteriorating the Koi’s quality of life. Remember that oxygen is essential to keeping your Koi alive and anything that affects it isn’t good for them. That includes heat.

What’s the ideal temperature range for raising healthy koi? Maintaining the range between 68-74 degrees will grow some beautiful Koi that you will want to show off to friends and family. You might even get the show-biz bug and start taking them to shows which a lot of Koi enthusiasts take part in. Who knows? Follow this guide and you will at least have some happy Koi fish that thrive in climate-controlled comfort.

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8 thoughts on “What Is The Best Temperature For Koi Fish?”

  1. I already got a Koi pond heater here so my problem now is the calibration of how exactly would the temperature be. I’d like to ask, what kind of tool or instrument should I use in testing the water? Can I just use the thermometer I’m using to check a baby’s body temperature during fever? Or, is there a special thermometer especially created for checking pond’s temperature?

  2. Thanks, Randall for this interesting post. It is good to know the facts about water temperature and what Koi Fish like the best. I found it difficult to have Koy in Australia because of the summer temperature gets very hot.

    It is doable but you need to have more water volume in your pond and not in the full sun in summer.
    If you get extended heat waves where the temperature is over 36 celsius for weeks at the time it is a struggle.

    • Hey Eric. Good day to you. Australia is definitely not the place I associate koi to be kept at. You could do your best to get some shade like building your pond under a tree, getting some blue dye to drown out the sun a little, lily pads and other pond plants, umbrellas, or other means of getting shade to turn the heat down.

      I’m not sure if even all of that could beat the Australia heat though. Thanks for stopping by.

  3. Wow, I have heard little about this fish and its really nice learning about its adaptation to temperature. Getting to rare animals require quite a lot of research so some of our action and inaction wouldn’t lead to the death of these animals, and that would leave the farmer at the losing end. Currently I’m not raraing this fish specie, I’m more into tilapia and cat fishes, but I’ll love to share this post so others can learn just as I have. Best regards.

    • Hi Chloe. How you doing? I love some catfish. The fried kind. Tasty. Did you know koi used to be farmed for consumption too? Not anymore, they are kept for their attractiveness. Earlier times were different though when there wasn’t grocery stores stocked with food.

  4. Hi

    That is one of the most important question that any fish keeper in ponds outside will want to answer.  The problem with  high or low temperature is that oxygen becomes less soluble as temperature rises, whilst solid salts such as nitrates become more soluble, which could effect the fish and more certainly the plants in the pond will flourish. This includes the weeds like algae and duck weed to take over the pond and then reduce the light available to the fish. It is quite complex.  October on the other hand is complex as higher temperatures can  promote  the growth of them, whilst very high temperature will kill them.

    Onr thing that surprises me is the temperature, as here in the UK we have koi outside where we can get serve frost and know they can survive them. Is this best for the KoI? Do you also recommend pumps to aerate the pond as well?



    • Hi Antonio. Good day to you.

      Maintaining the best temperature for koi isn’t too tall of an order. Koi can be very hardy fish as far as the weather is concerned. No deserts or places ice-cold year-round, but except those the conditions are fine for koi. Koi aren’t afraid of no frost either as long as you keep a hole melted in the ice above them from a de-icer. 

      I recommend ampond aerator on my shop page you can check out


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