Koi FAQs - Play It Koi

One of the reasons I enjoy the Koi Keeping hobby so much is that I continue to learn new things every day. There is so much depth to this hobby - the history, the culture, the biology, the science, the challenge, the beauty...It's an endless learning experience for all ages and my only regret thus far is that I didn't discover my passion earlier in my career. 

As a Koi business owner and evangelist for the Koi Collecting hobby, I get asked a lot of questions so I thought I'd compile a list of the most common questions I get. 

Have a suggestion for a question to add? Post on this blog or send us a private email ben@playitkoi.com

Q: How big should my koi pond be?

A: Our show pond at Play it Koi is an estimated 25,000 gallons. While this may be an ideal environment for koi, but may be out of reach for many hobbyists. The size of your koi pond will vary greatly depending on several factors. Budget, space available, the number of koi you want, how big you want you your koi to get and of course local building codes. Before we get into specifics, let's first define the difference between a koi pond and a water garden. A water garden is usually very shallow, has many plants and minimal filtration. Water gardens are usually a better home for goldfish than koi. A koi pond will be deeper, usually few or no plants and a more advanced filtration system. Generally, a minimum of 3 ft is best for koi and deeper is better, many will go 5, 6 or even 8 feet deep with their ponds.

A minimum of 1000 gallons is generally best. Some have built smaller ponds around 500 gallons and they have established a balanced system over time, but this is much harder to maintain.  

Q: How long do Koi live?

A:  The Japanese have koi that are well over 90 years old that thrive in their large mud lined ponds fed by natural springs. However, the answer to this question really depends on the environment the Koi are raised in, their diet, protection from predators, and of course genetics.  In Koi Ponds with high-end filtration and larger amounts of water, some hobbyists have gotten over 40 years from their koi. In most good quality backyard koi ponds, koi will live 20-30 years. 

Q: Can you mix large koi and small koi? Can you mix koi and goldfish?

A: Yes and Yes. Koi and goldfish are both types of carp, they will live side by side in perfect harmony. Also, large koi will not eat or harm smaller koi. Larger koi will eat koi eggs after a spawn and perhaps the tiny koi fry after they are hatched. But a 24" koi will not eat a 4" koi. The only concern with mixing large koi and small koi or goldfish is that the larger koi tend to get all the food and smaller fish don't get the nutrients they need to grow. So the small koi can stay small if you don't take care to make sure they are also getting food. Sometimes just switching to a smaller pellet is enough. Large koi can eat a small pellet without issue.

Q: How big can koi get?

A: Once again this is determined by the environment the koi are raised in, diet and genetics. Most koi will break 24" inside of 7 years. Anything over 30" is considered "jumbo" and many Grand Champions have been 36"+.  To grow koi large, you need two main things, lots of quality food and really good water. The problem is these two things often works against each other. The more you feed them, the lower the water quality gets, which slows the growth of the koi. But if you feed the koi less, you may have good water quality, but without the nutrients the koi won't grow. What you really need is BOTH. Really good water and lots of food. To achieve this you need great filtration, a large pond, and a low stocking density. This will allow you to feed the koi as much as they will eat without lowering water quality. However, to achieve "jumbo" size, you must also have great genetics.

Q: How does one determine the value of a koi over another?

A: It can seem strange to the new hobbyist that one koi can sell for $100 and another only slightly different looking koi can sell for $1000 or more. It's difficult to sum up what makes a koi valuable, but the easiest place to start is the koi show judging standards as these will dictate what the rest of us pay for koi. It's a competition where the koi are viewed and judged by a group of experts. Numerous winners are chosen including the Grand Champion. Just like in dog shows, the judges use a very specific, even rigid, set of standards to judge the koi. Body shape is by far the most important aspect and is worth the most points when judging the koi. Other attributes like skin quality, color and pattern also come into play. Each variety or type of koi also has their own set of standards for that variety. The value of the koi is often determined by how closely the koi fits into this set of judging standards and how well the koi would do if entered into a show. Koi that will do very well in a koi show are often referred to as "show quality koi" and these will sell for a much higher price. But beware, not all koi marketed as "show quality" actually are.

Q: Can you ship koi? How long can a koi live in the bag?

A: Yes, koi are shipped all over the world. At Play it Koi, we import most of our fish straight from Japan. Shipping koi domestically is much easier as there are no international customs to deal with. The trick is the pure oxygen in the bag. Oxygen is actually more important than water. The koi only need enough water to cover the body and the rest is pure O2. Generally its 1/3 water and 2/3 oxygen. With a little water conditioner, the koi can be in the bag over 24 hours. 

The koi will produce large amounts of ammonia while in the bag but a surprising thing happens at the same time, the pH drops very low. And the lower the pH the less toxic the ammonia becomes. This allows the koi to live in the bag water even though there are very high levels of ammonia. That is also why, after shipping, you NEVER want to mix any bag water with regular pond water. The result will dramatically increase the pH and in turn instantly make all that ammonia highly toxic to the koi. I have seen koi go belly up within minutes because somebody mixed pond water into the shipping bag.

Q: What is the difference between Japanese koi and domestic koi?

A: While it is true that domestic koi are bred from Japanese parents and have much of the same bloodlines, they are not always the same. First because the Japanese have about 200 years more breeding experience then we do. Also because to breed the best koi you must start with the best parent koi. But the absolute best koi never leave Japan so the breeders here in the US have a handicap right from the start. They simply don't have access to the absolute best koi genetics. However, it's not fair to say all Japanese koi are better the all domestic koi. There are low-grade koi even in Japan. What is fair is to say the very best Japanese koi are better than the very best domestic koi.

Q: What are Long Fin Koi (aka butterfly koi)?

A:  Genetically speaking longfin koi are practically indecipherable from standard fin koi. But they are different looking and therefore considered a different type of koi they have long flowing fins and tails. Longfin koi were developed by an Indonesian river carp. The river carp was genetically close enough to breed with standard koi and produce fertile offspring.  Longfin koi are hardier than standard koi (because they are not as many generations removed from that wild longfin carp) and many Japanese breeders have crossed longfin koi with their existing parent stock in order to make their bloodlines more resistant to parasites and infections. So even a koi that appears to be a perfect standard fin koi may have some longfin grandparents.

Q: Will koi survive ice cold winters?

A: Koi are a four season fish. They actually prefer to have a winter slumber where the water cools down and they stop eating. They are biologically programmed for this to happen. In fact, if a pond is deep enough, they can do just fine under the ice of a frozen pond. Just make sure you keep a hole in the ice for gas exchange.

Surprisingly more people run into problems in the summer than in the winter. Warm water holds less oxygen than cool water. Everything in the pond is highly oxygen dependent and it is a good idea to add additional oxygen to the water during the hottest months of the year, especially if the water might get into the upper 80's or even the 90's. The additional oxygen will cool the water and make sure everything in the pond is happy and healthy.

If you live in a region where you get extreme temps either hot or cold of both, then make the koi pond deeper. This will help stabilize the temps and insulate the koi from extreme weather.

Q: How much and how often should I feed the koi?

A: The frequency of the feeding will depend on many factors; Time of the year, the number of koi, the size of pond and quality of filtration. Koi do prefer to have more frequent small meals rather than one large one. Just like humans, we don't eat one giant meal in the middle of the day, we eat three smaller ones. Will we survive on one big meal a day? Yes, but it's not good for our digestion. Koi prefer the same thing, several smaller meals during the day.

During peak summer temps you can feed the koi as often are 4 or even 5 times a day, assuming the filtration can handle that much koi food. If not, still feed multiple times a day, just use smaller portions. You will find that the koi digest their food better and produce less waste, even if you increase to the amount of food per day.

Generally speaking, do not feed the koi if the water temps are below 50 degrees. low to mid 50's you can feed very lightly, maybe 2-3 times per week and only a handful of food. Upper 50's to low 60's you can start to feed once a day, but still small amounts. Mid to upper 60's you can start feeding 2-3 times a day and above 70 degrees, feed as much as the filter can handle.

Always feed a high-quality food with no fillers. Cheap foods often have fillers that are not as digestible and cause more waste. Most premium foods don't use fillers have are more digestible and therefore you will have less waste in the pond. 

Q: How do I know if my filter is big enough?

A: Frequent testing is the best way to monitor your filter. If the tests show 0 ammonia, 0 Nitrites and low Nitrates, then it is working properly and probably the correct size for your fish load. However, the fish will continue to grow and eat more food and produce more waste. A filter that has been fine for several seasons may one day not be big enough. This is very common for hobbyists who have numerous small koi in a small pond with a small filter. They are fine until the koi get bigger, then all of a sudden they start to have problems.

Usually, when somebody is telling me about their pond and I ask about the filter, the first thing they say is, "oh, but the water is very clear, the filter is doing a great job!". The clarity of the water really has very little to do with the health of the pond or the filter. Ammonia, Nitrites, DOC's and countless other toxins have no color and gin clear water may be toxic to the koi. And just the opposite is often true as well. Green murky water is often extremely healthy!

Q: Do I really need a UV filter?

A: Yes! Well, it's not a requirement, but it sure is a great filtration tool. A UV filter does far more than just clear up green water. Although it does get rid of green water very nicely! But it will also make the water more healthy. Aeromonas bacteria, the kind the causes bacterial infections, will pass through the UV and be destroyed. Also, every parasite has a stage in its life cycle where it is free floating and not attached to a host. If during that time they pass through the UV, they too will be destroyed. So a UV filter is very important for the general health of the pond. Even koi ponds that don't have a bit of algae can still benefit from a UV filter.

Please keep in mind that in order for a UV to be effective it needs to be properly sized for the flow from the pump. If water is pushed through too fast then the UV will not be effective. If it is pushed through too slow, then the bulb might overheat and burn out faster than expected. UV filters also need to be regularly maintained. The bulbs need to be replaced once a year and the Quartz sleeve needs to be cleaned off several times a season. Some UV's comes with wipers to make this easier.

Q: I don't want my koi, what can I do with them? Can I sell them?

A: The best way to re-home your koi is to contact a local koi club. They will usually be able to find a hobbyists that is looking to add some koi to their pond. Usually, it is considered a donation to the club, but knowing the koi is going to a good home is hopefully payment enough. If you are certain the koi have value and you want to try and get some money for the koi, you can always try your luck on eBay or Craigslist.


Have a suggestion for a question to add? Comment on this blog or send us a private email: ben@playitkoi.com


Koi keeping faqs




1 fish per 50 gallons as they get to be jumbo 1 fish per 250 gallons

Jackie DeHollander

Jackie DeHollander

how many Koi can I have in a 300 gallon pond-there are about 15 or so-the pond came with the house I bought and am wondering if there are too many-they are smaller ones

Leave a comment