Most koi fish outlive their owners, which is why the Japanese pass them down from generation to generation as a family heirloom. The oldest ever recorded koi carp reached 226 years old when she died in July 7, 1977. Although koi have significantly longer lifespans than other species, averaging about 70 years, this doesn’t mean all koi fish will reach over 200 years old.

How you take care of your pet fish and how well-maintained its environment would greatly affect the health of a koi. If you’re wondering how to extend a koi’s life, here are 20 solutions to the most common and some uncommon questions you might have about taking care of koi fishes.

Koi Pond and its Ecosystem

A koi’s environment ensures your pet fish is happy, healthy and thriving. Your heart might be in the right place, but some errors like overpopulating a pond, adding harmful plants, or not adding extra security from predators may unintentionally make a koi sick, injured, or even die.

A lot of People will start asking that how many pet fish can my koi pond handle?

Koi Pond in House Garden

Koi Pond inside House Garden

Having a lot of koi in your pond may be a good idea, but since these gorgeous carps need plenty of space to exercise, explore, and grow to their full-sized potential, the koi load should be your first consideration when building a pond. Any number of baby koi could fit a typical 3,000-gallon pond, but after 2 to 3 years, it will become overpopulated as your pets grow to impressive adult sizes. Aside from pond square footage, water depth and total water volume also help in determining just how many koi your pond could handle.

Having males or females would also factor in. Compared to a male koi, female koi also have more body mass as it ages. Generally, experts recommend one adult-sized koi for every 250 gallons of well-maintained pond water.

Second, is it possible that I can add plants on and around my pond?

When you add plants to a koi pond, it increases oxygen production in the water and makes the pond water well-aerated. Plants also provide shade, keep water cool in the summer, prevent spreading of algae, and help female koi choose a perfect surface to attach fertilized eggs. Plants can be a natural filtration system for your pond, but not all plants would work.



Water Lilies

Water Lilies Floating Plant

Floating plants like Hyacinth, water lilies, Lotus, water Poppy and water lettuce give shade to your pets, while submerged (or oxygenating) plants such as fanwort, American waterweed, and Ludwigia (water purslane) add oxygen to water while removing excess nutrients (like CO2 or nitrites). Floating plants may not like forced movement if your filtering system includes a jet. If you try it and leaves or parts of the plants fall into the pond, sink down and mush at the bottom, you have to clean them manually every time.



In addition, parasites on plants could be introduced to the pond without your knowledge and affect the health of your koi. Algae control would also be impossible if you increase salt levels to the recommended 4% because it would cause plants to die. The best of both worlds would have to be a plant shelf, where a container (or shelf) is built along the edges of the pond with a barrier to keep koi from eating the plants, or leaves falling into the pond.

Are my koi protected from predators?

Predators, such as birds, wild animals, or amphibians, could eat your koi if you are unaware of their intrusion. Depending on where you live, foxes, raccoons, muskrats, otters, beavers, opossums, or sometimes even bears could eat your koi. Birds, specifically Kingfishers and Herons, can wipe out an entire pond within hours.

Common Kingfisher




Snapping turtles and large bullfrogs may become a predator to your fish if your pond is near a creek. If you’re still in the planning stage of a koi pond, you can build a pond with enough depth and hidden structures below for your koi to hide in when danger strikes. If the pond is already built, you could cover it with netting at night to deter predators. Other techniques that have worked for other koi pond owners are decoys and repellents.

Water Quality for Koi Pond

You may start to ask how frequently should I change pond water?

Water changes is necessary since most ponds have a closed-water system (no drainage), which means whenever water evaporates, pollutants are left behind. In most cases, the filtration system removes pollutants or partially treated. However, this may not be enough for those with a huge pond, plenty of koi fish or plants, excessive algae production, and many other factors such as local climate, type of filtration system, and more.

The consensus in the koi pond community is that partial water change is important at least once a week. Changing 100% of your pond’s water would be traumatic for your koi, plants, algae, and even bacteria on the pond. But the amount is largely debatable, with recommendations as little as 5 to 10% weekly water change to 40% to 50% of your pond’s water every week.

Performing a water quality test gives you an idea of the pond’s amount of ammonia, nitrite, phosphate, and chlorine, as well as pH water levels, salinity, alkalinity and general hardness, which in turn help you decide how much water to remove.

After a while the pond water turned green and what is the cause? Is my koi okay down there?

The most common reason why pond water turns green is due to algae. Sometimes, the pump or filter isn’t enough for the pond’s size. If your pond is located in full view of the sun, algae bloom more productively. Fortunately, algae don’t hurt your koi directly.

Koi Pond With The Color of Pea Soup

Koi Pond With The Color of Pea Soup

Two types of algae commonly exist in koi ponds. One of it is phytoplanktonic (free floating) and second is Benthic (attached) algae. The first type is the one that makes your pond water green or look like “pea soup.” It mostly occurs during spring and in newly built ponds without sufficient bacterial population yet.

Benthic or attached algae such as water net, horsehair algae, blanket weed or string algae are harder to control. Whenever you manually remove them from your pond, they leave reproductive spores in the water, which will continue the algae production cycle. Solutions for algae include vacuuming accumulated sludge, adding biological treatments, increasing salt, installing ultraviolet sterilizer, or using algae control products like AlgaeFix.

If your pond is still newly established, avoid chemicals and give your filters time to work (even if it takes up to a month) for the pond to have a balance of beneficial bacteria.

What can be the cause of my koi fish died and my pond water very clean?

Clear water on your pond isn’t a guarantee that it is healthy for your pet fish. Contrary to this idea, ammonia, nitrite and nitrates that may be present in your pond water are all colorless, but could cause diseases in fish. High levels of nitrite or ammonia have even been recorded to kill koi by weakening their immune system to death.
To prevent this, you have to test your water regularly. There are no safe amounts of nitrite or ammonia, which is why these toxins must be zero when tested.  To correct nitrite, you should add 0.2% salt for every 1ppm nitrite.

For ammonia, all you need to add is an ammonia binder/remover. Of course, the best way to ensure healthy ponder water for your koi is to provide it with a sufficient filtration and pump system that is appropriate for the size of your pond.

Seasons and Climate Changes

During freezing winter season, do I really need to transfer my koi?


If you have a pond at least 30-feet deep with plenty of space to hide, your koi will mostly be safe in water during winter. However, this refers only for adult-sized koi, since those under 4-feet long without much fat could not survive in cold temperatures. The better solution for small-sized koi would be to transfer them indoors, or install a pond heater (which can be costly to use).

Although the topmost part of your pond water could completely freeze, the ice isn’t the main cause of koi deaths during winter. The culprit is reduced oxygen combined with increased toxic gases from ice-sealed surface that could lead to koi health deterioration or death. If transferring adult-sized koi indoors, or using pond heaters aren’t favorable solutions, you need to prepare the pond for winter by setting up a sufficient aerator with proper ventilation.

If your pond is located in an area with harsh winters, you might also need to purchase and set-up a thermostatically-controlled de-icer, which prevents water to freeze throughout winter. If you already have an appropriately-sized aeration system for your pond, but pond water still freezes, you can change placements of your aerator (in the middle of the pond) in order to stir water gently. Since water at the bottom is generally warmer during winter, the stirring ensures a natural balance for koi even during harsh climates.

Note that it is never a good idea to break ice if the surface of your pond freezes. The force may traumatize your koi, or worse, hurt them during the impact.

How should I spring-clean my pond?

Preparing your koi pond for spring is important because the transition from winter to spring can be dangerous to your koi. As cold-blooded fish species, your koi is unable to control its body heat, which is why it relies on its ecosystem. From feeding your recently-winterized koi to monitoring water temperature, there are quite a few guidelines you must follow.

First of all, clean the pond

If your koi pond has rocks at the bottom, you would need to remove them and clean debris before putting them back. Most experts don’t recommend rocks on koi ponds because they breed harmful bacteria and require regular cleaning that could cause koi trauma.

Second, ensure the water temperature is stable

Before adding chemicals, feeding koi, or doing anything to disrupt the pond’s balance, the water temperature should be around 10 to 13°C. It is best to use a floating pond thermometer to get accurate results.

Third, deal with parasites and harmful bacteria

Your koi will begin moving more once water stabilizes, but its immune system is still weak from the cold winter, so it is best to address parasites and harmful bacteria before introducing koi food again. A broad spectrum treatment like ProForm-C and parasite worm treatment like Koi Prazi are non-chemical and both less toxic to koi.

Fourth, re-start filter

If you stopped using your filters throughout winter, now is the time to restart them. Clean any waste left inside the filter, then restart your pond’s nitrogen cycle by running your filters back on.

Last but not least, encourage nitrogen cycle with good bacteria

If your spring gives water temperatures over 10°C, you can skip this part. But for the rest who would find it hard to re-establish the nitrogen cycle of your pond, adding good bacteria like Niigata Water Bio Balls (which contains 20 billion bacteria per tablet) can improve nitrogen cycle more rapidly.

Is there any Fall/Autumn preparations I need to do for my koi pond?

If your pond is located near trees, or you’ve lined up plants along the shelf, you should install leaf netting to keep leaves off the water. Once leaves decay under water, it could affect the ecological balance of your pond and cause a wide range of health problems for your koi. You can also use a pond vacuum to clean accumulated sludge at the bottom.

Depending on how harsh winters are in your area, and the type of aeration system you have installed, you can turn off the filters and pumps in preparation for winter. Outside filters won’t work, since the water-transporting tube could freeze exposed in that environment. This also goes for other external filters, external pumps and UVs. A de-icer and an aerator would be enough to continue source of aeration throughout winter.

Koi Diet

Feeding Koi Fish

How often should I feed my koi?

How often your koi need to eat depends on various factors, such as size/age of your fish, and local climate (that affects water temperature). Koi have better appetites and are generally more active during warmer weather (about 15.5 to 29°C), so an adult koi may need 2 to 4 times a day feeding to make up for its active day. However, spring and autumn water temperatures (10 to 15.5°C) require less feeding. You can give them food every 2 days.

During winter when water temperature rises to 32°C, koi tends to conserve energy and in turn, require barely any food, so you could stop feeding. Don’t worry though, since your koi could find food in the pond, and it takes koi about 4 days on average to digest food.

The general rule about how much food to give your koi is to give them only what they could consume within 5 minutes. Experiment on the amount of food. If there is food left after 5 minutes, it means your koi is already full. The food will only sink below and decompose into mush.

 What types of koi food are allowed/not allowed?


Feeding Koi with Watermelon

Feeding Koi with Watermelon

Koi eat just about anything. It eats plants, insects, small bugs, algae, and store-bought fish food. It can even eat people food like shrimp, cereal, peas, rice, lettuce, and more. However, most koi pond owners prefer to soak pellets with water, which are made to provide specific nutritional needs of koi.

Soak Pellet ( Koi Food)

Soak Pellet ( Koi Food)

To ensure your koi ages with its beautiful bright colors intact and receive optimal nutrition during specific times of the year, you need to consider their environment when choosing food to give them.
During summer make sure the temperature of the pond is around 15.5 to 29°C water temperature because your koi would be the most active in warm water, so it requires high-protein food.

As winter season raise the temperature of the pond to 32 degrees or above water temperature because koi’s metabolism reduces in cold water, you won’t need to feed them throughout winter. They could find enough food, such as algae, growing in the pond. If you’re really worried about your koi during this time, you can choose Manda Fu Koi Food, which is known to provide digestion rat eof 98.2% even in water temperatures as low as 7°C.

Manda Fu Koi Food

Manda Fu Koi Food

As Spring/Fall make sure the temperature is around 10 to 15.5°C water temperature. Your koi is still adapting to the water temperature’s transition from freezing cold to natural levels, and would only begin becoming active when water becomes warmer. As such, you could feed low-protein, or wheatgerm-based food around this time.

Koi pellets available in the market indicate which season they are most applicable. Worms, frozen food, and other nutritious treats are also offered as supplements for koi’s day-to-day food.

 Should I change my koi’s diet?

Changing your koi’s diet relies largely on water temperature levels, which means you should change their diets during winter (in areas where water temperature dips below 10oC during winter), and spring (as the water temperature transitions back to normal). While you might feel like you’re abandoning them during cold harsh winter, note that koi remain motionless near the bottom of your pond and stop actively looking for food. Forcefully feeding them when water temperatures go below 3.9°C can be harmful to the koi’s digestive systems and could lead to metabolic disorders.

You can re-introduce your koi’s regular-season feeding program when the pond’s water temperature averages 10°C. You don’t have to rush feeding them once winter is over. You still have to reactivate filters, clean the pond, make sure there are no parasites and harmful bacteria, and re-establish nitrogen cycle – all of which ensure that pond’s water quality is high. Once you’ve done all these steps after winter, you can now begin reintroducing food to your koi.

Breeding Koi

Koi Breeding

Koi Breeding

How old should my koi need to be to spawn?

 If you’re excited about breeding koi, but don’t know if your koi is sexually mature or not, it may be best to seek the help of a professional breeder. Unless the koi in question hatched and was nurtured under your care, the age when you got a koi from the market is impossible to know.

In addition, some koi may exhibit spawning behavior, even if they do not have the ability, drive or sexual maturity to reproduce. These reasons make identifying age tricky for non-breeders. Experts, however, can identify a koi’s age by checking out its ear bone.

Do I need to seek the help of a professional if I want my koi to breed?

Koi could naturally breed on their own in the spring and summer seasons. Technically, you can leave your koi alone and hope for the best that a resulting offspring (referred to as “fry”) joins your pond. The problem with letting nature run its course though is that regardless of the vast number of eggs produced, other koi could eat them before fry could hatch from the egg.

Koi Eggs

Koi Eggs 46 hours After Fertilisation

Like most fish, koi reproduce through spawning (wherein a female koi lays numerous eggs and one or more males fertilize them). This process is tricky and requires careful attention, from choosing parent koi, to nurturing fry separate from adult koi. If you are committed to breeding koi, you should learn everything you can about brood stock, propagation, egg incubation, and fry nurturing. However, if you are unable to set-up a spawning tank, or have no time to attend to this entire process, it is best to let expert breeders handle it for you.

Koi Diseases and Prevention

Koi Fish

Koi Fish

How do I know if my koi pond fish has parasites?

Except for anchor worm and fish lice, almost all other parasites are microscopic, which means there is no way to find out if your koi has parasites. However, there are quite a few signs that will help you identify if your koi has parasite issues.

 Yawn-like gesture with often indicates that koi is trying to remove parasites from its gills. Scratching and swim fast with regular rubbing off on the edges of your pond, rocks or other textured surfaces. The fish will Hanging around the surface or waterfalls and also could be also showing of low oxygen in the water.

The fish show missing scales from “scratching.” The koi fish will keep jumping out of the water but could also be a sign of poor water quality. If you witness two or more of these signs, it is most likely that your koi is suffering from parasites.

What is the cure for koi parasites?

There is no single treatment for koi parasites, mainly because there are various types of parasites that could affect your koi’s health.

Fish Lice

Fish Lice

Fish Lice attacking Koi

This parasite punctures your koi’s skin and eat off its blood. While lice can multiply on the pound laying over 500 eggs at a time, it could take up to a month for them to hatch. The good news is that you have time to deal with these lice.

Dimilin -X

Dimilin- X

The bad news is those baby lice can feed on koi blood quickly after hatching and even before you could actually see them. The most effective and quickest treatment for fish lice is Dimilin and IDI.

Anchor worm

Anchor Worm on gill

Anchor Worm on Gill

Although the treatment for anchor worm is the same as fish lice, it affects your koi differently. When you see a Y-shaped string at the end of your koi’s body, this “string” is actually a female worm with her head buried in your koi eating and two egg sacks (with hundreds of eggs ready to hatch in about 2 weeks).

Gill or body flukes

Flukes infection on gill

Flukes infection on Gill

These parasites are extremely common and deadly because its feeding of your koi could lead to worse bacterial infections. They feed on koi’s blood by poking tiny holes through the slime coat of your koi. When the body flukes are finished feeding, the hole left makes your koi susceptible to bacterial infections, ultimately causing deadly ulcers (open body sores).

Aqua Prazi

Aqua Prazi

Gill flukes, on the other hand, target your koi’s gills, which affect your pet fish’s breathing ability. Experts recommend using Aqua Prazi as a safe, affordable and gentle treatment for gill and body flukes.

Deadly Microscopic Parasites

Epistylis Disease

Epistylis Disease

Costia Disease

Costia Disease Under Microscope

Some of the most common microscopic parasites that are koi killers are costia, ich, trichodina, Chilodincella, and Epistylis. They have different methods of hurting koi, but their common denominator is that these parasites can kill koi very quickly. Fortunately, treatment only involves salt; it’s cheap, safe and natural.

If you find the 0.9% salt treatment process of around 3 days to 2 weeks as pretty long, you can use Terminate in not only treating all kinds of microscopic parasites, but also to cure fungus infections.

 My koi has white spots. Can this be a sign of Ich?

Ich Disease

Ich Disease

White Spot Disease (or Ich parasite) is a protozoan that grows in a pond with poor water quality, then attaches to koi gills during maturity. Ich is microscopic, but you can barely see it as tiny white grains of salt attach to the koi. This small parasite can kill baby koi quickly, and cause bacterial infections on adult koi since they feed on koi’s tissues by digging into your pet’s skin. These parasites feed on a koi for over 3 weeks.

Malachite Green

Malachite Green

Aside from dealing with your pond’s water quality issues, you can also increase salt levels of the pond, improve aeration, and increase water temperature to up to 27°C. In dire conditions, you may also quarantine a part of your pond for up to two weeks and use 1.5mg of malachite green for every liter of water (or about 6mg for every gallon) for every hour.

Scales of my koi look like they’re swelling (or inflamed). What should I do?

Dropsy disease

Dropsy disease / Pinecone Disease

Your koi may have dropsy and also known as Pinecone disease, which is caused by a bacterial infection that has infiltrated your koi’s liver or kidney through the blood stream. In rare occasions, dropsy may be caused by Mistraspora cyprinid, a rare fish parasites that feeds on koi kidneys. Regardless of the origin, dropsy results to kidney enlargement and ultimately, kidney failure.

Symptoms of dropsy include swelling of a koi’s body may due to fluid retention, bulging eyes, pine-cone shape or raised scales, loss it of balance when bacteria reaches bladder, and isolation or swimming toward parts of the pond with high oxygen levels. Unfortunately, since dropsy is the final stage of bacterial infection, it means the affected koi cannot be treated any longer. The good news though is dropsy is not contagious, which means it normally affects one koi at a time.

Debride RX

Debride RX

However, the root of dropsy (whether by parasites or bacterial infection) can be contagious, but you’ll have time to quarantine the pond or introduce medications like Debride RX or MedFinn before another koi suffers the same fate as your sick koi.

My koi has a fluffy, greenish bump on its fin. What is it? Can I remove it?

Fungal Infection on Koi


 Your koi might be suffering from fungal infections, which is often caused by poor water management or overcrowded ponds. Some koi are susceptible to these kinds of infections during periods of high stress.

Saprolegniasis is known as fungal spore. It is the most common fungal infection that affects koi.

Saprolegnia or water molds will grows on water temperatures ranging from 0 to 35°C and often attacks koi with an existing injury. It appears in different colors from green, yellow, brown to white. It is often raised, fluffy, irregular bumps or as cotton-like growths on the fins, gills, skin, eyes, or koi eggs, and have a green tinge due to the algae growth on fungus.

If caught early, most fungal infections can be treated and cured with Chloramine-T or small doses of salt treatment on the quarantined area. They are not typically contagious, so only one koi at a time can be infected. However, prevention is key to avoid fungal infections completely.
After removing the infected koi from the main population, you should clean your pond, replace old filters, test water quality, monitor other koi on your pond, and avoid making drastic changes to the water temperature. You should also keep pH levels of water at level 7 and transfer some of your koi (if you have an overpopulation issue) to improve their immunities and reduce changes of fungal infection.

 Is there a way to prevent KHV disease?

Originally called KHV (koi herpes virus), Cyprinid Herpesvirus 3 (or CyHV-3 for short) is a disease specific to koi and other carp (Cyprinus carpio) varieties. It presents very similar symptoms to herpes, but its infection mainly occurs through the koi’s gills. Symptoms may include gill discoloration, infected gill tissue, sunken eyes, pale patches of skin, loss of mucous coat, and thin appearance. Later stages of CyHV-3 could lead to gill and kidney damage.

Koi inflicted with this disease can become lethargic, swim erratically, or suffer from skin erythema. Because damages to the gills leave koi with less oxygen, they often go to areas of the pond with higher oxygen levels, such as waterfalls.

Unfortunately, CyHV-3 has no available treatment. Once a koi gets the virus, it could either die or survive and become a carrier of the disease (and spread it to other koi on your pond). It is also extremely hard to prevent this disease, since the virus only becomes symptomatic at high water temperatures.
This means a KHV-carrying koi could appear healthy in the store where you bought it, but show symptoms once you add it into your pond at a lower water temperature. This is the reason why KHV outbreaks have affected the koi trade in the past. Your only safeguard is to quarantine any new koi before introducing it to your pond’s ecosystem.

Wrap Up

 Koi are beautiful creatures that live up to an average of 50 years. Original Japanese koi fish has been a symbol of luck, prosperity and good fortune within Japan, which is why it has a long history as a top choice for gifts or passing-down to one generation to the next. Koi is an interesting carp species.

Kumonryu Koi

Kumonryu Koi (Black Koi)



It could even recognize you when feeding them and swim near you every time you go to check out the pond. Varieties of koi are dependent upon its color. Most popular ones include kumonryu (black koi), kigoi (all-yellow koi), goshiki (orange and white), and kohaku (red and white koi). Maintaining a koi pond has its pros and cons. It gives you a zen-like outdoor spot and provides an excellent landscaping opportunity with options for waterfalls, plants on shelves, and a whole lot more.

Chilling out near the pond even has therapeutic benefits. However, maintaining the water quality of a pond, taking care of every koi that lives in that pond, and monitoring their health through seasonal changes, bacterial growth, infections, and other issues can be quite challenging. But if you like the science behind proper water management, the intricacies of breeding koi, treating unique koi health problems, and you are willing to spend quality equipment for sufficient aeration system, filters, pumps, koi food and supplements, your koi could live a long, happy life.

And if you’re lucky enough, the koi can even serve as a priceless heirloom for your next generations to come.


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