Keeping Koi Cool in Hot Temps

Services for Real Estate Pros with Kodama Koi Farm

Japanese Koi are cold-water fish. Their ideal water temperature is between 70-78 F. They become stressed as temps creep up to and past the 90's F. Many things happen when the water temperature rises that affect the health of your koi. Does this mean you can't own outdoor koi in Arizona, California or other states with very hot summers? No. But, it does mean you have to be extra vigilant during these heat waves, and you have to take several precautions long before. Let's see how we can set your friends up for a comfortable life wherever you live!


Keeping the temp lowered is the best first defense. Tall hedges on the west side of the pond, or an arbor built over the pond itself, can go a long way to reduce heat stress. Having a trellis over the water pump means you aren't pumping boiling hot water into your cooled down pond. Lilly pads can be used to shade the fish, but plants in koi ponds in general are very tricky and can cause many problems so MAKE SURE YOU HAVE AN EXPERT HELP YOU SET UP POND VEGETATION!! 


Low oxygen levels: Koi fish become stressed when oxygen levels reach 4 ppm, and start to die at 3 ppm. At around 90 F only 7 ppm can dissolve in freshwater. This is a scarily thin cushion- a small swing can cause big problems and your fish could suffocate. Having a deeper pond means temps below stay cooler and better oxygenated. Extra aeration is highly recommended, you really have to err on the side of caution with this one. Having a waterfall  increases aeration but you MUST have a high quality filter system for koi pond, especially in these hot temps! Also, counter-intuitively, plants can create problems with oxygen levels. During the day they release oxygen, but at night they consume it. This means they compete with your fish for what may be already very low O2 supplies. Early morning fish die-offs are the most common because of this. So either keep your vegetation separate from your pond ecosystem, or make sure it is designed and monitored by an expert.


Increased parasite breeding: Warmer temperatures significantly increase parasite breeding rates. Fish lice can spread throughout the whole pond in just days. These and anchor worms can be seen with the naked eye, but others, such as flukes, cannot. Get comfortable taking scraping samples and taking a peek under the microscope. Our very extensive Koi Health Blog will help you become an expert in quickly identifying and treating diseases. Early detection and treatment is ALWAYS important, but even more critical when the temperatures rise.


Death of Biological Filtration: Your biological filtration relies on O2 and thus start to die off when oxygen levels get low, as they do when temperatures peak. This means your well balanced ammonia, nitrite and nitrate levels can start to vacillate and quickly get out of hand. Make sure you are being extra vigilant in checking your nitrogen levels in your pond to save your koi friends from suffering. Understanding the nitrogen cycle of your koi pond is of the utmost importance!


We want to help people all over the U.S. fall in love with the hobby and art of Koi. We hope to make it easy to understand so it can be a rewarding and peaceful time for you and your loved ones. 



Comments (1)

Leif Price
Chirpy Home - Portland, OR
Blogger at Chirpy Home

Lovely fish they are! Sharing this one to a friend who has them in her yard.

Aug 21, 2019 06:02 PM
Kodama Koi Farm

Thanks! We appreciate it and the koi will too lol. We have to speak for them since they cannot and make sure people understand what stresses them out and what makes them happy :)

Aug 30, 2019 05:51 PM