Spring Time and Koi Ponds - What You Should Know - Play It Koi

Alas! The birds are starting to tweet, Water lily shoots are rising through the water column, frogs' are starting to croak, and your beautiful koi fish that have been dormant for the last 4 months are now starting to swim around and flash their colors in the sunlight. 


Hooray, We Finally made it! Springtime is Here!

But "what should I be doing with my pond in the spring?" This is a common question we receive from many Play It Koi customers. And this article tries to summarize what you can expect of your koi pond in the spring...

Spring is a critical season for your pond, especially with regards to pond temperatures and koi and goldfish. After a long winter of cold water temperatures, not eating and sometimes less than ideal water quality, koi and goldfish are low on energy and susceptible to parasites and bacteria. During the winter months when water temperatures are below 40°F, a koi's metabolism slows down and their immune systems are dormant. Luckily, pretty much everything else in the pond is dormant during the winter too... including the ‘bad’ disease-causing bacteria such as Aeromonas / Pseudomonas as well as many common parasites.

Welcome to Aeromonas Alley!

Once the pond water begins to warm up in the spring, therein lies probably the toughest and potentially most dangerous time your fish will face all year. This spring ‘danger zone’ is often referred to as ‘Aeromonas Alley’ which is when the pond temperatures are between 50°F and 65°F. As your pond temperature reaches 50°F these bad bacteria begin to grow and multiply in the pond much faster than the fishes’ immune system can fight them off. In fact, fishes’ immune systems are only working at 50% efficiency when the water temperature is 65°F. The optimal temperature for a Koi fishes immune system is around 73°F to 74°F.  To make things worse, many common parasites such as Costia, Chilodinella, Trichodina, and Flukes also begin to rapidly grow at the same time.

Keep Your Pond As Clean as Possible!

If you cleaned your pond properly last fall, this greatly increases the chances that your koi fish will be ok. Most parasites and bacteria thrive in ponds with lots of sludge and organic matter at the left in the bottom. If you don't own one already, do yourself a favor and buy a Pond Vacuum (they literally pay for themselves in as little as 1, sometimes 2 cleanings by a commercial business)

During the spring, water quality can also be a problem. The good bacteria that live your pond and filter (Nitrosomonas and Nitrobacter) that break down harmful ammonia and nitrites multiply very slowly compared to other bacteria, especially in cool water. It is always a good idea to feed your fish sparingly in the spring when temperatures are cool and feed them only a good wheat-germ based diet. We do not recommend feeding any sort of Growth Formula Koi food that is typically heavier protein content and harder to digest at this time of year.  

Lastly, and probably most importantly, be sure to monitor water quality. Ammonia, nitrite, and pH are obviously your basics for koi ponds. For these, something basic and inexpensive like API's Master Liquid Test kit will do most pond owners just fine. However, for those around the Pacific Northwest, please pay particular attention to kH as our water here is notoriously low and it is critically important not only to support your Koi fishes continued growth but also for buffering the pond water from wild pH swings which can be fatal. 

Keep a Close Eye out for Signs of Stress

If you notice any signs of stress or unusual behavior with your fish (I.e. Flashing, separating themselves from their school, not eating, rubbing against other objects, not eating, or anything out of the norm) It's time to take a closer look. If any of your fish have a parasite or bacterial infection, treat immediately. The sooner you can curb the problem, the better because if you catch an infection at an early stage, there is a much greater chance of successfully treating it.

Signs of bacterial infection are red sores, lesions, ulcers, fin rot, mouth rot, and red streaks in fins and on the koi's body. Ulcers usually start at the site of an injury, the bacteria then infect it causing further damage, and fungal infection can also occur. For those that have not treated a bacterial infection with koi before, our professional advice is to call a vet for your first time. Some vets do house calls, and some will have you capture the fish and take them in for assessment. We recommend a house visit if your doctor offers it, but this is usually the more expensive option as well. With all bacterial infections, your goal is to keep the koi's habitat as clean and pristine as possible.

An Ounce of Prevention...

AquaMeds makes a great product called MedZyme which specifically is designed to keep the bad Aeromonas Pseudomonas bacteria populations down. We at Play it Koi have used this product each spring for the last several years and have had excellent success. Our recommendation is to start treating the water when the water gets as low as 40 degrees °F and all the way through Aeromonas alley which ends at around 65 °F. 

If you notice any signs of parasite infection, we recommend you properly diagnose and understand what parasite you are dealing with prior to choosing your treatment path. The only way to do so is through a skin scrape or gill scrape and check it under a microscope. Common signs of parasite infections are white spots on fins and body, a greyish film patches on body, excess mucus/slime coat on fish, fins clamped close to the body. The purpose of this article is not to go into different forms of parasite identification and treatment. That's an entirely different article in its own. However, the two most common treatments for parasites include: 

Prazi: for Flukes  (note, this often sells out in springtime very quickly)

Malachite Green & Formulan: for Ichthyophthirius (Ich), Chilodonella, Costia, Oodinium, Trichodina, fungal & fungus infections (note, these are only safe to use in water temperatures are above 50 °F.)

Where do Pond Parasites Come From? 

Unfortunately, Parasites live in almost every pond. And if they don't now, they probably will sometime in the future. The saying, "there is no such thing as a sanitized fish" is absolutely true. Even the most careful of Koi collectors find parasites unavoidable as they are bought into our systems by visiting animals and wildlife.

Both predators and pests can bring all sorts of harmful bacteria, fungi, and parasites to a fish pond unless you implement deterrents. Herons which are hunting fish and ducks who visit the pond are two of the worst culprits, with both being capable of spreading a wide range of disease and parasites. Flukes are often brought by the feathers of the bird, or the eggs may have been present in the feces of the animal. Preventing predators and ducks from entering your koi pond will help stop parasites and bacteria spreading, and will also help with both stress and water quality.

Another common way flukes may get into your water is when you introduce new fish or plants to the pond.

Important Pond Temperatures

  • Below 40°F:  Watch for flukes! Keeping a hole in the ice for the pond gases to escape is important.  But watch out, as it's then when the eggs are laid by flukes.  This means flukes that infect koi in winter lay their eggs and remain dormant throughout the season, and then start to hatch in huge numbers in spring. Even if the flukes themselves die off, their eggs will remain and start to spread when water temperatures rise. Think AquaMeds Aqua-Prazi
  • 48°F and above:   Aeromonas – ulcer-causing bacteria become active and multiply rapidly. Treat Proactively with MedZyme or other Aeromonas killing treatment. Flukes are also reproducing.
  • 50°F: Nitrosomonas a good bacteria in your pond and filter that convert Ammonia into Nitrite becomes active. Think Microbe-Lift PBL (professional Blend Liquid)Costa is a common, yet hard to spot pond parasite begins to reproduce quickly. Flukes are also reproducing.
  • 50-55 °FKoi and goldfish should have ‘awakened’ and begin to feed. Their immune system is starting to work again. Start using cold water bacteria to jump start filters with good bacteria
  • 58°F:  Nitrobacter is another good bacteria that converts Nitrite into Nitrate in your pond is becoming active. Think Microbe-lift Night Out II  or AquaMeds Summer Blend.
  • 60-64°F: Other parasites become active (Ich, Trichodina, and Chillodonella). Think Malachite Green
  • 65°F: Fishes’ immune systems are getting stronger – up to 50% of full strength and can fight off most typical bacterial and parasites in the pond if water quality is good. THINK WEEKLY WATER CHANGES! 

But It's So Tempting to add fish! Can't I Just add 1 or 2 now?  

Our phones start ringing off the hook the moment the sun begins to shine... Trust us. We get it. It's hard for us to wait too. But years of experience have shown us that it is in your best interest to wait until your pond warms up more to add more fish. 

Once your pond warms up above 65°F, the chances of your fish becoming sick are much reduced. As long as proper pond maintenance is performed and water quality is maintained, you should enjoy a trouble-free pond season. But if you start adding new fish before this time, sadly more times than not, you will end up regretting it.

Lots of other koi fish stores may not be as forward in sharing this same information because frankly, it's bad for business.  There is a lot more profit to be made for a store if you keep coming in every few months to replace your koi. However, at Play it Koi, we are in it for the long term and know that we are only successful if our customers are happy.

Koi are beautiful, majestic creatures that can last a whole lifetime if you are thoughtful, careful and do it right. Our goal is to help you get there and to be able to enjoy the hobby as much as we do. Wishing you the best! 

- The Play It Koi staff

Springtime for koi fish ponds




If a koi fish or gold fish is sick do I take it out and treat it in an aquarium by itself



Flukes are all ready living on your koi. All it takes are stressors for them to multiply out of control. So they do not have to be brought in from external sources to create a problem.

Cheryl Curran

Cheryl Curran

Love this! Thank you very much for sharing

Justin Oliver

Justin Oliver

This is a great place to purchase pond products. They have been very helpful to me in the past few months being I’m a new pond owner

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