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Why Quarantine?
The quarantine and treatment of new fish is probably the single most important activity koi owners need to do to ensure the health of their ponds and fish.

Newly purchased Koi could possibly still carry viruses, parasites, bacteria, fungus etc., even though your Koi dealer did their very best to eliminate these. Koi is affected by stress, much like us human beings.  Netting, placing them into bags and transporting them are all stressful and exhausting for them. (See article on stress) Koi go through the same stress when transported to and from shows. This affects the koi’s immune system, making them more susceptible to disease. Keeping and treating new Koi in a separate quarantine tank for at least 21 days is the best way to decrease the risk of disease before introducing them to your main pond. In addition this will give your new Koi a chance to rest.

The occasional ulcer or fin rot is explainable. But when it comes to massive fish kills or pond-wide health problems, the most common reason for these sad events is usually linked directly back to the pond keeper’s failure to properly quarantine and treat new fish prior to introducing them to the pond.

So Basically the following are the reasons for quarantine:
  • Isolate new fish so that their health and condition can be properly evaluated,
  • Isolate fish when returning from a show.
  • Reduce the stress of the new fish in its new environment
  • Treat the fish as required.
  • Prepare the fish for the new pond.
  • Isolate sick or diseased fish to prevent further spread of the problem and provide an easier way to treat the fish.


For the purpose of this article, we will focus on the quarantine procedure for new fish. As stated above, the minimum requirement of a quarantine process is 21 days. You may ask yourself why 21 days? Well actually it can be 21 days or indefinite. It all depends what transpires during the quarantine process. The determining factor will be the condition of the fish, water temperature (this determines the life-cycle of parasites) and the possibility of a viral infection that may take a long time to surface. The temperature is critical in relation to the quarantine period, as using a lower temperature could mean that some problems and symptoms may not become apparent until some point in the future when higher water temperatures are encountered by the infected fish. I believe that Koi bought in the autumn appear to settle in nicely, until they experience higher water temperatures in the spring or early summer. This is particularly the case with bacterial/viral problems that may be dormant in the Koi in cooler water, and require higher temperatures to exhibit clinical symptoms.

What is required of a good facility?
Maintaining a good environment for the fish in quarantine is an absolute essential. The quarantine facility should provide impeccable water because in a smaller system, the margin for error is decreased. If this cannot be achieved it is far better to place the fish directly into your pond and take your chances. A good system requires: -
  • A suitably sized container, at least 500 liters. It can be bigger depending on the size and number of the fish to be quarantined. A depth of 500 cm to 1 meter is sufficient because you need to observe the fish
  • Any kind of insulation of the pond to reduce temperature variations (bubble wrap works well).
  • Secure covering with a net.
  • A sufficient size and well matured filtration system.
  • Heavy aeration.
  • Temperature control (heating).
  • Good lighting (Remember you must observe the fish)

If you know you are going to be purchasing fish ahead of time, set up the quarantine tank before hand and have the pump, filter and air stone running. Use water from your main pond. If not possible, use de-chlorinated water. Using filter material from your main pond system can create a mature filter. Add regular baking soda to buffer the pH in the quarantine facility. Your fish will adjust to your pH. The temperature in the quarantine tank should be around 23 to 24 degrees Celsius. If it is not warm enough, it is now time to add the heater. We found that koi is very skittish when released in a small facility. By creating one or more hiding places for them you can calm them down almost instantly. We use normal orange bags weighted down in small bundles. It is an excellent hiding place for them but it makes monitoring them more difficult.

When you get the new fish home float them in the pond, still in the bag of water, for at least 20 minutes . Do NOT open the bag during this time. If the fish has been in the bag for a long period of time or shows signs of stress and if the water in the pond is only a couple of degrees difference, it might be best to skip floating the bag and just put the fish right into the pond.

When a fish has been in the bag for a couple of days (imported fish), the water in the shipping bag will have a low pH.  The low pH actually protects the fish because the lower the pH the less toxic the ammonia is. In such a situation, don’t start pouring pond water into the bag, because the ph will rise and the ammonia will become more toxic.

When the floating time is over, remove the fish from the bag and put it in the pond. It is advisable to NOT add the water from the bag to the q-tank. Whatever pathogens the fish is bringing with it is also in the bag of water and it is better to reduce the odds of problems and just pick the fish out of the water and turn it loose.  Use your hand or a net to remove the fish from the bag. (The water in the bag will have a lot of ammonia in it and can possibly contain lots of bad bacteria, parasites (eggs or cysts) and fish feces.

Now make sure the pump and air stone is running and cover the pond securely with the net. Fish will definitely try to jump during the following couple of days and will do a fatal flop if the net is not properly secured. Observe the fish and make sure that their gill movement is even and not labored. Fish should stay upright when swimming and when resting. The last step before you have a rest is to give them a good dose of LEAVE THEM ALONE. Do not feed at this stage. Let the fish settle down and get used to the new pond and water.

Day two do a partial water change because by now the fish has excreted all the excess ammonia and you can now start adding salt. You will need a total of 3 kilograms of salt for every 1000 liters of tank water, but at this stage add only 1 kilogram per 1000 liters. On day two we normally also start treating for bigger parasites like fish lice, anchor worm and flukes by adding 4.4 ml of Seponver Plus per 1000 liters. We do this because these parasites need to be eradicated before they start laying eggs. Seponver Plus will remain in the water for two to three days.

Day three. It is now time to thoroughly examine the fish. Use a shallow tub for this process. At a minimum, perform the following tasks:
  • Check water parameters. This should be a daily procedure and the parameters should be managed accordingly.
  • Raise the salt level with a second dose of 1 kilogram per 1000 liters, to .2%.
  • Do a general external exam, checking the fins, mouth area, skin and gills, eyes, etc. Also feel the belly and make sure it is firm. Check for visible macro parasites, such as lernea and anchor worms. These should be gone by now.
  • Next, examine the gills. Slip your thumb under the gill cover and raise it gently. The gills should be blood red. It is not uncommon for a stressed fish to expel blood from its gills during handling. Sometimes it seems that there are hunks of gill material also in the blood. While this is not a good thing it is a common occurrence. The increased blood pressure caused by stress forces blood out from the gill filaments and normal clotting of the blood seems like hunks of gill material.
  • Do a scrape with a microscope slide, cover the specimen and examine under the scope. Obviously we are looking for anything that is moving, such as parasites and flukes. This is a critical step in the quarantine process, as this will dictate the routine to follow in the next couple of days. Without a microscope, you have to assume that the fish has parasites and flukes and you need to go through a wide spectrum of treatments.
  • Last, check the fish feces. Feces is either light gray or brown (depending on the diet), narrow and tubular and firm. If the feces are whitish and stringy, a possible internal parasite problem may exist.
  • You can feed them at this stage. If the food is still in the water after 20 minutes, remove it.

Day four: This is the time to begin the treatment of the fish for other parasites not affected by the treatment on day two. The microscope study should determine the routine to follow but if this has not been done, we have to assume that the fish has EVERYTHING. This is not a bad assumption and as such, treatment for all conditions should be performed.
  • Perform a 20% water change and treat the water accordingly.
  • Add 2 kg of salt per 1000 liters that were replaced, plus the third dose of 1 kilogram per 1000 liters. The salt level should therefore be raised to .3%.  Check the fish’s behavior. By this point he should have settled down and acclimated to his environment.
  • Add the appropriate dosage of Antibac, manufactured by Loolilicks and distributed by your local koi dealer.

Day five: Effect daily water changes and maintain the salt level at 0.3%. This level should be maintained for the next couple of weeks, by adding 3 kg of salt for every 1000 liters water that is replaced

REMEMBER while in quarantine no amount of ammonia or nitrite is acceptable. High levels of ammonia will kill fish very quickly, but even low levels will increase the stress of the fish and will lead to all kinds of complications.

Day seven: The following needs to be performed:
  • Check water parameters and treat accordingly.
  • Scrape and scope the fish.
  • Check the gills.

Day ten: If the scrape and scooping did show parasites treatment should now be effected for the specific parasites and quarantine period will be prolonged.

Assuming that the scope studies show nothing and the fish’s behavior is normal, you can start planning for the fish’s release. To do this, perform the following:
  • Perform a 50% water change using water from your main pond. This will start to introduce the fish to the main pond’s condition. Try not to use tap water with de-chlorinator because a future Potassium treatment will then be ineffective.

The next step is of the utmost importance. After the 50% water change, add one or two fish from your existing pond to the quarantine facility. This will reveal if any of the fish, whether your existing fish, or the new arrivals are immune to something, but remains a carrier of some disease that can contaminate others.
  • Keep the temperature above 24 Degrees Celsius
  • Maintain a .3% salt level
  • Observe the feces
  • Continue to feed lightly.

Day twenty-one: Last days in captivity. Prior to release, perform the following:
  • Complete a thorough physical exam, especially the gills.
  • If you have the facility, do a scrape and scope.
  • Treat with Malachite green/formalin mixture.
  • After four hours release the fish in the main pond.

Enjoy your precious living jewels!

Koi don’t like to be alone and if you have purchased only one fish, always place a “kamikaze” fish in the quarantine pond for company. Furthermore, if a newly purchased fish shows signs of disease, postpone the quarantine protocol and concentrate on the existing problem. After all, that is what quarantine is for.

Last Updated on Thursday, 17 February 2011 20:09