Koi Basics

Koi Pond Guidelines...

Raising koi in a backyard pond can be a very enjoyable hobby. There are some considerations, however, that you must take into account before adding koi to a pond. Adult koi can grow up to 3 feet in length, which means they require a significantly larger pond than do goldfish. It is recommended that you provide at least 1,000 gallons of swimming area for each koi, but who are we kidding? If we all followed this way of thinking then we would need a 3,000 pond just to accommodate three koi. A more realistic guide is to base your stocking of koi on your pond size, filter setup, and overall water quality.  Bottom drains are absolutely essential for a proper Koi pond. 

A koi pond must be at least 24” deep; however, a minimum depth of 4’ is recommended. This depth is important because koi will remain near the pond bottom during the cold winter months. Shallow ponds may freeze over, causing fish to suffocate and die during the winter. I recommend making your pond at least 4 feet deep, although I realize this is not always possible. Try to make your pond as deep as possible. Trust me; your fish will thank you for it. The deeper your pond is means the more gallons of water it can hold, which in turn means you can stock it with more koi. Koi are extremely hardy, but proper filtration is absolutely essential if you want them to reach their full potential.
 

Buying Koi Online…

Personally, I was always a bit hesitant to purchase Koi online. At first glance, the idea of paying hundreds (or thousands) of dollars for a fish you have never seen in person to a dealer you have likely never met sounds just a tad, shall we say, insane. But after years of coming to know a few dealers from the various forums I belong to, my attitude has started to change. By far, the most important aspect to consider when purchasing Koi online is the dealer himself. Does the dealer have a good reputation? Are his Koi healthy? Do his Koi look as good in person as they do in the pictures? These are all very important questions that must be answered before dealing with an online Koi dealer.

Another important question you should ask an online dealer, especially one who specializes in Japanese imported Koi, is whether or not the Koi you want to purchase are actually in the country and available for sale. Often times dealers who make frequent buying trips to Japan will post photos of Koi that still reside in Japan. It may be several weeks before these Koi are actually imported to the U.S. and then another month before these Koi are quarantined and actually ready to be shipped to your pond. Dealers may ask for a deposit in order to reserve these Koi for you, but be sure you are comfortable with the deposit amount being requested. I’d say that $100 per Koi is a fair deposit. Anything more than that and I start to feel a strange tingling sensation in my stomach.

Imagine leaving a $500 deposit with an online Koi dealer, only to learn 6 weeks later that the Koi you intended to purchase has died. If the dealer is honest, and most seem to be, he’ll refund your money. But realistically, you just gave him a no interest loan for 6 weeks. Plus, if you’re like the vast majority of us, that $500 could’ve come in handy once or twice. I know of one online Koi dealer who requires a deposit of half the total cost of the Koi you wish to purchase. This seems a bit excessive to me and is not something I’m personally comfortable with. If you feel differently, more power to you.  Koi are not added to our online store until they have arrived, been QT'd, and are actually available for sale. 

Feeding Koi…

During the warmer months, we feed our Koi 6 – 8 times per day. During the cooler months, we cut back feedings to once or twice a day. The general rule of thumb is to never feed your Koi more than they can consume in 5 minutes. This prevents uneaten food from decaying in the pond and causing water quality issues. 
 

Koi Stocking Levels...

Koi stocking is definitely a touchy subject. Ask 10 koi keepers what the ideal stocking rate is and chances are you’ll receive 10 different answers. Most of koi experts seem to recommend a maximum stocking rate of one koi per every 250 gallons of pond volume. The only problem with this standard, however, is that it doesn’t take human nature into account. Raising koi can become quite addictive and this can lead to a pond becoming dangerously overstocked if you’re not careful. Trust me; I know what I’m talking about.

To be honest, I haven’t met many pond owners who actually adhere to this rule. Most of the koi keepers I’ve met keep their ponds considerably overstocked, and surprisingly, their Koi appear to be thriving. It’s important to understand that 250 gallons per koi is considered the ideal; not a hard and fast rule. Most pond owners can and do overstock their ponds without ever encountering any problems. The real answer to the Koi stocking question is “it depends.”

Personally, I try to limit the stocking rate in our Koi ponds to one Koi per every 200 gallons of pond volume. Bear in mind; however, that my ponds are equipped with an oversized DIY filter setup and I’m not raising jumbo show-quality Koi that cost thousands of dollars.

In July 2005 I met a nearby pond owner who purchased 8 small koi shortly after building his 500-gallon backyard pond. Five years later those same 8 koi grew to well over 16” each and seemed incredibly cramped in such a small space. He ended up giving me three of his koi for free just to make things less crowded in his pond. He could have easily sold the koi for at least $200 each, but instead he opted to give them away because the load created by 8 large fish was wreaking havoc on his filter setup.
 

Routine Pond Maintenance...

It is very important to test your pond water regularly for ammonia, nitrites, nitrates and PH. Ammonia and nitrites are both extremely toxic to fish, especially at high PH levels. While nitrates aren't toxic in themselves, a high level of nitrates can greatly contribute to fish illness. It's a good idea to always keep some ammonia detoxifier on hand in case the ammonia level ever gets out of control. Ammonia and nitrite readings should remain zero at all times. Nitrate levels should always register below 300. PH should always be above 7.0; 7.6 is considered ideal.

Beware of the dreaded PH crash, which can be caused by simply leaving the hose running. If PH quickly falls below 6.5, your Koi will start to die off almost instantly. I’m speaking from experience here, so heed my warning! PH readings above 8.0 can be deadly when ammonia is present. High PH levels where no ammonia is present; however, are harmless.

Depending on your pond volume, I recommend doing 10% water changes on a weekly basis. If you’re using city water, be sure to add declorinator. In reality, you can probably do without using declorinator if you only doing 10% water changes, but if you have expensive Koi, I wouldn’t risk it.
 

Caring for Sick Koi...

The best defense against sick Koi is a healthy pond. This means it is properly filtered, not overstocked, and always using effective QT procedures. What are QT procedures, you ask? I’ll get to these in a minute.  If you suspect parasites in your water, the very first thing you should do is add salt to your pond. Add one pound of salt per every 100 gallons of water. Continue this treatment daily for three days then gradually lower the salt concentration in your pond by doing partial water changes once a week. Salt kills most of the parasites you can't see.

The type of parasites you can see, namely fish lice and flukes can be killed with Dimilin.  If you have a Koi pond, you should definitely invest in a microscope.  Learning how to scope your Koi for parasites is a skill every pond owner should have.  When treating a pond for parasites it's important to treat the entire pond and not simply remove an ill fish and treat him in a quarantine tank. If one fish is infected, rest assured several others are as well. Dimilin treatment should be repeated 7 - 10 days after the initial treatment to ensure all parasites are effectively killed off.

One clue that your pond may be infested with parasites is when your koi exhibit "flashing" behavior. No, flashing doesn't mean your koi are exposing themselves. Flashing actually refers to koi that quickly flip themselves over to rub against sides of your pond. When the sunlight hits the side of a koi you see a quick reflection of sunlight; called a flash. Another good idea is to examine your koi on a regular basis, checking for any visible parasites.

Also look for exit wounds, which are usually small brownish red spots on the koi where a parasite attached itself to the koi. I've had good experience using both salt and Dimilin in the past. I also purchased an antibacterial dip called Tricide Neo, which wasn’t cheap, that is known to rapidly heal ulcers in Koi caused by bacterial infections. Unfortunately the Koi I treated was already too far gone and luckily I haven’t had a need to use it since.

Ulcers will likely heal by themselves if you maintain good water quality and don’t overstock. If your Koi has bulging eyes (pop eye) and/or has scales start to pinecone out, it is probably too late. This condition is called “dropsy,” which basically means that one of your Koi’s internal organs has become infected. I have seen this happen in the past as well, and it wasn’t a pretty sight.

Probably the best advice I can give if you find yourself caring for a sick Koi is to visit KoiVet, which is listed on our Links page. Someone there will be able to help you, I promise. Some of the more advanced Koi keepers actually inject antibiotics into their Koi when they’re sick, but I doubt I’ll ever reach that level.
 

When to Add Koi to a Backyard Pond...

It is not a particularly wise idea to add Koi (or goldfish for that matter) to a backyard pond during the dead of winter. I actually learned this lesson the hard way due to my own personal experience. Although koi can survive harsh temperatures, they need adequate time to adjust. It is best to add koi during spring, summer, or early fall. This will give them adequate time to adjust to the pond water before the temperature drops.

If you find a particularly nice Koi around Christmas time that you absolutely can’t resist taking home, be sure to use proper QT procedures – preferably in a heated environment. I use a heated 180-gallon aquarium and DIY quarantine tank in our backyard shed for this purpose. A common misconception is that koi are cold water fish. Technically speaking, this is not the truth. The reality is that koi do best in temperatures between 64 – 74 degrees. Koi and goldfish can survive cold temperatures, but only if they are given ample time to adjust. Sudden temperature drops are often fatal to koi and goldfish.
 

Breeding Koi in Backyard Ponds...

Our Koi had a flock spawning in May 2007. Of the millions of tiny fry that actually hatched, of these, only 300 or so actually survived to reach 2” in length. Most of these will be given away or sold cheaply to local pond owners.  A recap of our 2007 flock spawning is available in our Pond Diary.
 

Pond Filtration...

A good filter system is absolutely essential to a healthy Koi pond.  You can view plans of our own DIY pond filters in our DIY in our DIY Projects section.

 

Keeping Ornamental Fish in Koi Ponds...

My favorite types of ornamental fish include black moors, red cap orandas, and ryukins. Other types of ornamental fish you may also be familiar with include fantail goldfish, bubble-eye goldfish, and lionhead goldfish. Ornamentals, much like koi and goldfish are cold water fish. Raising ornamental fish can be just as rewarding as raising koi. While it is often tempting to do so, I do not advise adding ornamental fish to an established pond with koi or comet goldfish for several reasons. Ornamentals are very slow swimmers, which makes it difficult for them to compete for food with faster fish. Another drawback to keeping ornamental fish in the same pond with koi is they may become snacks for the larger koi if they get hungry. I have a few black moors now with missing eyeballs, which were bitten off by hungry koi when I kept them all together in our small backyard pond. Ornamental fish are also not as hardy as koi or goldfish, which means they may not survive if left in an outdoor pond during the cold winter months. I have about a dozen ornamental fish myself, which I move to our indoor aquarium in the fall and return to our small pond in the spring.
 

Keeping Tadpoles and Frogs in Koi Ponds...

Large koi and goldfish will eat basically anything that will fit into their mouths. This includes tadpoles and small frogs. If you wish to add tadpoles to your pond and expect to see them grow into frogs, then you will have a lot of problems if there are already large koi living in the pond. I have a small pond that I use exclusively for raising tadpoles and ornamental fish. You may have better luck raising tadpoles in a pond with smaller koi and goldfish, but they will eventually grow up and you’ll end up with the same problem later on. You will have the exact opposite problem if you add a large bullfrog to a pond containing small koi or goldfish. Like large koi, bullfrogs will eat anything they can fit in their mouths.
 

Keeping Aquatic Turtles in Koi Ponds...

Turtles, especially baby turtles eat fish. You should never add turtles to a backyard pond with koi. Doing so would be an invitation for disaster. If you wish to raise turtles then it would be best to give them their own pond, without any koi present. It is also important to put up a fence around a turtle pond to prevent the turtles from wandering off. You should bury the fence at least 6” below ground to prevent the turtles from digging out. Turtles also require a way to crawl out of the pond so they can bask in the sun; a small island is perfect for this. Turtles are also extremely messy so an excellent filter setup is critical to keep the water clean. I recommend adding small feeder goldfish, rosy red minnows, and mosquito fish to a turtle pond. Doing so will help to control algae growth and guard against insects. Of course, many of these fish will also end up as snacks for the turtles from time to time. Our 800-gallon backyard pond was built especially for aquatic turtles.
 

Keeping Mosquito Fish in Koi Ponds...

I highly recommend adding mosquito fish to any backyard pond. As their name suggests, mosquito fish are great for helping to prevent mosquitoes and other insects from laying eggs in your pond. Mosquito fish are quite hardy and can survive year round in a backyard pond. The only possible drawback to adding mosquito fish to a backyard pond is the rate at which they can reproduce. If you add a dozen mosquito fish to a pond, chances are very good that you will have a few hundred mosquito fish swimming around within a few months. Stocking your pond with koi and goldfish, who eat mosquito fish from time to time, helps to keep the population of mosquito fish in check.
 

Keeping Rosy Red Minnows in Koi Ponds...

Rosy red minnows are often sold as feeder fish at pet stores. They are great for helping to control algae growth in ponds. Like mosquito fish, rosy red minnows are extremely fast breeders. They aren’t quite as hardy as mosquito fish, however, as a significant percentage of them may die off in the winter if left in an unheated backyard pond. Out of 50 rosy red minnows in my backyard pond, approximately half survived through the winter. The ones that died would swim over my pond net and couldn’t figure out how to get back down again into deeper water, thus they froze to death near the pond surface.
 

Adding Tropical Fish to Koi Ponds...

Unless you live in a tropical climate, you should never add tropical fish to a backyard pond. Tropical fish require a constant temperature of 74 – 86 degrees Fahrenheit to survive, whereas koi and other cold water fish require a far lower temperate of 54 – 74 degrees Fahrenheit but can survive even when temperatures reach well into the low 20s. Tropical fish will surely perish in a backyard pond when the temperate drops below 54 degrees Fahrenheit for a prolonged period of time.

It is also not a good idea to keep tropical fish along with cold water fish in an indoor aquarium for the same reason. I’ve actually broken this rule myself, however, so I guess it’s okay if you do the same. I have two pictus catfish living in our indoor aquarium, which also doubles as the winter home for our ornamental fish. So far we haven’t had any problems keeping them together. I guess it depends on the temperament of the actual fish involved. I tried to add two puffers, but they were far too aggressive as they kept picking at the fins of my ornamental fish. I ended up giving them away to my stepfather after just a few hours.
 

Adding Native Fish to Koi Ponds...

I don’t know of anyone that has trout or sunfish living in their backyard pond. Based on what I’ve read, I doubt these fish would do well in a backyard pond because they require a constant temperature that is only possible in large natural bodies of water. Trout, like koi, are members of the carp family so I guess they could technically survive in a backyard pond under ideal circumstances. Never, and I do mean never, add bass to a backyard pond. Bass are extremely aggressive fish and they would surely tear up any koi or goldfish living there.

I had three 10” bullhead catfish living in our koi pond for quite a while and they got along fine with our Koi, but I doubt I’d add any more in the future. At one point I thought about adding some native sunfish to our koi pond, but ultimately decided against it. I definitely wouldn’t recommend adding any bass to a backyard koi pond as they are extremely aggressive and would surely torment your Koi. I suppose you could add some trout to a backyard pond, but why would you want to? Koi are much prettier to look at and have a personality to boot.