Common Koi Diseases and Treatments

Any fish breeder knows the importance of being knowledgeable about the different types of fish diseases, as well as the appropriate treatments. This is especially true for koi fish owners and breeders. Here is a short review of the most common koi fish diseases and the treatment options:

  1. Ich. This is among the most common diseases both for tropical and cold water fish. The Ich is a protozoan that can grow and multiply in an outdoor pond. The protozoan attach itself to the gills of the koi. Ich appears as white spots on the body of the koi fish and feeds on the koi’s tissue. For smaller koi fish, the infection of Ich can be fatal.

Treatment: to treat Ich, increasing the concentration of salt in the water to 0.5% for a couple days has been known to kill Ich. Increasing the temperature to around 70 degrees Fahrenheit while at the same time increasing aeration can also help in killing this protozoan. Another method would be using malachite green and formalin, which should be mixed in the water with a ratio of 1.5 mg malachite green for every liter of water.

  1. Costia. This is a type of flagellate that multiplies rapidly is considered a parasite. Koi fish infected with costia will seem lethargic. They will also try to rid themselves of the costia by rubbing on the sides and bottom of the pond. The infestation will also make the skin of your koi fish appear white or gray. The infection could even be observed in the gills of the koi fish.

Treatment: like in treating Ich, malachite green and formalin can also be used in treating Costia. Potassium permanganate is also effective as well as a salt bath with 3 per cent concentration. Likewise, trypaflavine and copper are effective treatments. Trypaflavine should be used with a 1 ml to 1 liter ratio while copper should be used with a 2 ml to 1 liter ratio. Overdose must be avoided.

  1. Anchor worm. This is a parasite that also digs into the skin of the fish. The anchor worm is a crustacean and only the female anchor worms attach to koi fish. The damage it inflicts on the fish can cause irritation and further lead to bacterial and fungal infection.

Treatment: anchor worm can be manually removed by using tweezers. After the anchor worm has been removed, the infected area should be rubbed with Neosporin. Make sure to treat the pond with Dimilin or Dylox before releasing the koi fish back to the pond.

These are just a few of the common diseases that infect koi fish and the corresponding treatments. There are many other diseases that may infect your koi fish overtime and, as such, it is important to be very observant. At the first sign of symptoms, you must consult with experts or identify all the signs to determine the disease.

How to Differentiate Male and Female Koi

If you are a new koi owner or breeder, the first thing you would probably want to know is how to tell whether a koi fish is male or female. This task might seem daunting at first, but knowing the differences between the male and female koi fish will make sex identification a breeze. Here are the differences that you should take into consideration.

  1. Size and shape. The male koi fish is slender and shaped like a torpedo. The female koi, on the other hand, are considerably fatter around the abdominal are. They are also wider and rounder in shape. While this characteristic is usually sufficient in identifying the sex of the koi, you need to consider other factors as well, such as the koi diet, its genes, and various other environmental factors. These can affect the size and the body shape of the koi fish. As such, this factor may not always be accurate.
  2. Fins. Observing the shape and size of the fins of the koi fish can also help in determining whether it is male or female. The female koi fish has a generally larger fin. However, its fins will have fewer colors and a more rounded shape. On the other hand, the fin of the male koi fish tends to be sharper rather than rounded on the edges. It will also have a comparatively more solid color.
  3. Excretion hole. There is also a difference between the excretion holes of the male and female koi. In the female koi, the excretion hole will be more prominent, with a pale pinkish color, while in the male koi, the excretion hole will be more sunken. The color is white rather than pale pink.
  4. Cheek surface. The cheek surface of the male and the female koi also differs. The female koi will have smooth cheeks. The male koi, will have a rough cheek surface.
  5. Tubercles. During breeding time, it will be much easier to identify the sex of your koi fish. Male koi fish will start developing tubercles or white spots. These small spots will be highly concentrated around the gill plates and should be easy to spot.
  6. Breeding time. The most obvious indication, of course, will be observed around breeding time. Obviously, the fish that will spawn and lay eggs will be the females. You will also observe that the male koi will chase a female koi during this time (this would basically be the equivalent of courting for koi fish). If you ever spot a koi fish bumping the back end or the side of another koi fish, chances are, the one doing the bumping will be a male koi.

Please note that the differences between the male and female koi fish will only start to become evident once they are old enough. If you are not sure whether the koi you intend to purchase is male or female, it pays to ask the seller directly.

How to Protect Your Koi Pond

Having your own outdoor pond can be risky, especially since it will be harder to regulate the water conditions. If you plan to build a pond for koi fish, the last thing you would want to happen is to lose them by accident or because not enough precautionary measures were taken. To keep your koi pond safe, I would recommend the following:

Keep your fish safe from predators

Having a shallow pond will make your koi fish easy preys to predators, so it is a common rule of thumb to give your pond plenty of depth. If this is not possible, the next best thing would be to make sure that your koi fish ample amount of hiding arrangements. This can be done by placing tunnels or a large amount of vegetation in the pond which can serve as a great hiding area. You can also provide your fish with floating vegetation. Floating vegetation shields your fish from most predators as it will be much difficult to see the fish.

To protect your pond at night, it is always wise to install a light which helps with deterring predators such as neighborhood cats. If at all possible installing a pond that can be viewed from a window gives you the ability to keep your eye on it more conveniently. Also, make sure that the edges of the pond are steep and that the water is deep enough.

Deter predators

Deterring predators can be effected in a number of ways, depending on which ones you have in your area. You have a wide range of options to choose from, some of which are:

  • Installing a net over your pond during the night or whenever you are away.
  • Setting up alarms to scare away predators.
  • Building a fence around the pond to keep children and other predators away.
  • Provide predators with alternative food sources and water. (this is not always the best choice)
  • Set up scarecrow sprinkler systems. This is motion activated and will help deter flying predators.
  • Set up a decoy. Predators will not venture into a place if they see their own predators in the pond. You can install fake alligators or snakes near the area.
  • If you have a dog, give it access to the pond so that it can chase away predators. Dogs are good at chasing birds, raccoons, and other wildlife away and can help a lot in protecting your koi fish pond.
  • Have an ultrasonic device that produces sounds unpleasant to wildlife. This will keep predators away without being detrimental or disturbing to people.

Bear in mind that in order to effectively determine which method you should employ, the first thing you have to do is figure out the kind of predators lurking in your area. This will allow you to correctly assess which methods to use.

If the situation gets out of hand, do not hesitate to contact and seek help from your local animal control unit.

Koi Pond Aerator 101

If this is your first time to setting up an outdoor pond, then the most important thing you need to know about is proper aeration in the pond. This is particularly true if you are setting up your own koi pond as the koi, the plants, and even the bacteria will need a steady supply of oxygen. So how do you set up your koi pond aerator? Here are some tips that you should keep in mind.

  1. Location. The first thing you need to know about is the placement of your koi pond aerator. For the best results place your aerator within the bio filter system. If this is not possible, put the oxygen pump, as close as possible where bacteria will not commonly be found. Another option would be to install the bio filter within a water fall feature, if you have one within your Koi Pond.
  2. Air volume. Depending on the stocking levels, the volume of air needed will vary. Generally, the air to water ratio that should be followed is in the chart below:
  • At least 40 liters of air for every 1000 gallons of water
  • At least 80 liters of air for every 2000 gallons of water
  • At least 120 liters of air for every 3000 gallons of water
  • At least 160 liters of air for every 4000 gallons of water

How aeration works

As you can see, the ratio should be 40 liters of air for every additional 1000 gallons of water. This ratio will allow for the maintenance of safe and healthy levels of oxygen in your outdoor koi pond.

Additional guidelines must be kept in mind. This is because the volume of oxygen that the water can hold varies depending on temperature, salinity, and even atmospheric pressure. The important reminders are the following:

  • Less oxygen is held in the water as temperature of the water increases.
  • If you have a lot of koi fish, or if you have aquatic plants in the pond, the amount of oxygen in the water will decrease. This is because the more living things there are in the water, the more oxygen will be consumed.
  • Not only does oxygen retention decrease as water gets warmer, the respiration rate of fish increases. To make up for the oxygen deficiency, more oxygen should be supplied.
  • Too much food given to koi fish will only lead to decay, which uses up the oxygen in the water. The same goes for a large number of aquatic plants in the pond.


Caution must be observed when installing the aerator. Remember that the air pump itself should never be installed below water level unless a check valve is installed. Not only will installing a pump below water level be problematic should power supply be interrupted, it also increases the risk of electrocution.

Air pumps often come with a step-by-step guide in installation and you should follow the instructions. If you can, ask someone from the shop where you purchases the pump to install it for you.

Koi Bridge

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