For hobbyists, there’s nothing quite as exciting as introducing a new koi or goldfish to your pond. While it’s often tempting to add a new fish directly to your pond as soon as it arrives at your door, doing so is a risky move.

It’s important to take necessary precautions to keep your new fish and your existing pond population safe and healthy, and that involves following proper quarantine procedures. Our quarantine guide will tell you everything you need to know about when, why, and how to quarantine your koi and goldfish.

The Importance of Quarantining

There are several reasons why it’s imperative to quarantine your new koi and goldfish. First and foremost, the shipping process is stressful for your fish. When koi and goldfish are stressed, their immune systems are weakened, which makes them more susceptible to illness. Any bacteria or viruses that may be in your pond could potentially make them sick–even if there isn’t an active outbreak. The quarantine process lets your fish adjust to its new environment slowly and recover from the stress of transport, which results in stronger immune function and decreased chance of illness.

Additionally, the quarantine process lets you monitor your new fish for any signs of illness. While reputable dealers maintain strict health and biosecurity measures to decrease illness, stress from the shipping process can weaken fishes’ immune systems and make them vulnerable to attack. Quarantining allows you to monitor your koi or goldfish for any signs of illness, treat any issues that may arise in isolation, and reduce the risk of contaminating your pond.

Quarantine procedures also apply to koi and goldfish that are already established in your pond population. If a fish displays signs of illness, it can be moved to a quarantine tank for treatment to reduce the risk and cost of an outbreak spreading to the entire pond.

Setting Up Your Quarantine Tank

The environment of your quarantine tank should mimic that of your pond as closely as possible. Think of your quarantine tank as a mini version of your pond that requires the same attention and care. Recreating the pond environment will help make your new koi or goldfish’s transition from quarantine tank to the pond as stress-free as possible.

It’s recommended that you set up your quarantine tank at least a month before your new fish arrives. This is because biological filters need about a month to begin working effectively. Biofilters use living organisms to convert unwanted ammonia and nitrites into less harmful nitrates using the nitrogen cycle. However, a source of ammonia needs to be present in the quarantine tank to initiate the nitrogen cycle and activate your biofilter. The easiest way to do this is to add feeder goldfish or other types of inexpensive fish to your tank to produce waste.  Without waste in the tank, there is no nitrogen, which means no biological filtration. If you add fish before your tank’s nitrogen cycle has been established, you run the risk of exposing your koi and goldfish to toxic levels of ammonia and nitrite, which can be extremely harmful to their health.

To put together your quarantine tank you’ll need:

  1. A tank (usually ~100–500 gallons)
  2. Filter and pump
  3. Air pump
  4. Tank heater (if quarantining in cooler temperatures) and/or pond shade
  5. Net cover for tank
  6. Salt
  7. Pond thermometer and water test kit


Your tank should be at least 100 gallons, but it usually doesn’t need to be any larger than 500 gallons. If you’re quarantining more than one fish at a time, use the standard equation of 1 gallon per 1 inch of fish to determine an adequate size for your needs. It’s important that the tank is made of plastic, rubber, or PVC. It’s best to avoid galvanized tanks, as they can be harmful to your fish.

Filter and Pump

Your tank will need a filter and a pump. Many hobbyists think they can skip filtration since the quarantine tank is a temporary environment for the fish, but having a filter is critical to keeping the water in the tank clean and your fish healthy.

Mechanical filters remove solid waste, while biological filters remove nitrites and ammonia from the water. Most mechanical filtration systems provide some biological filtration capabilities, which is typically sufficient for your quarantine tank. Consider adding a stand-alone biological filter for more heavily stocked quarantine tanks.

Again, the sooner you get your filtration system up and running, the better. The pump should be large enough to circulate all the water in your tank every 30-45 minutes.

Air Pump

Your fish and your biofilter both need oxygen to stay healthy. Your air pump should be positioned above your tank with at least one air stone placed on the floor of the tank. If you have a dissolved oxygen (DO) meter available, it can help ensure that the oxygen levels in the water are adequate.

Tank Heater and Pond Shade

Because quarantine tanks are fairly small, they are more susceptible to rapid changes in temperature, which can be harmful to your koi and goldfish. The optimal temperature for your quarantine tank is between 72-74°F. To maintain this, it can be helpful to add a small aquarium heater to your tank, especially if your setup is outside or in an uninsulated garage during cooler months. A 300-500 watt heater should suffice.

Small, shallow tanks are very susceptible to rapid warming as well. Your quarantine tank should be set up away from direct sunlight. If it’s difficult to avoid sunlight, make sure there is some source of shade in your tank.

Net Cover

Koi and goldfish can be jumpy when they’re stressed. Covering your tank with a net will ensure that your fish don’t escape the tank while adjusting to their new environment.


Salt can ease stress in koi and goldfish and help combat any parasites that may be present. It’s suggested to maintain a 0.3% salinity in your quarantine tank, which can be achieved by adding 3 pounds of salt per every 100 gallons of water. Digital salt meters are inexpensive and make monitoring salt levels easy.

Pond Thermometer and Water Test Kit

The water quality in your quarantine tank is extremely important. Consistently monitoring water parameters will help you ensure that the environment is remaining suitable for your koi and goldfish.

Quarantining New Koi and Goldfish

When your new fish arrives, there are a few things to keep in mind while adding your koi or goldfish to the quarantine tank.

Adding Fish to the Quarantine Tank

Your new fish will arrive in an oxygenated bag. Before adding your fish to the tank, float the bag on the surface of the water for 20-30 minutes. This will allow your fish to slowly acclimate to the temperature of the water. Be sure to cover the bag with a cloth or towel if it’s going to be in direct sunlight. While your fish is in the bag, do not add any water from the tank to the bag. Doing so can throw off the chemistry of the water, which can be harmful to your new fish.

After 20-30 minutes have passed, release your koi or goldfish into the quarantine tank. Try to avoid getting any water from the bag into the quarantine tank. Once your fish is safely in the tank, cover it with a net immediately.

Quarantine Protocol

It’s recommended that you quarantine your new fish for a minimum of 14 days. During this time, you should closely monitor your new koi or goldfish for any signs of illness or disease.

If possible, one or two fish from your pond should be added to the quarantine tank as canary koi to help you monitor for any bacterial, parasitic, or fungal issues. The idea, similar to a canary in a coal mine, is that any illness dormant in your pond or in your new fish will impact the canary koi and vice versa. If any issues arise, you’ll be able to identify and treat the problem without it impacting your entire pond population.

Do not feed your fish for the first 48 hours they are in the quarantine tank. It’s common for koi and goldfish to lose their appetite when they are stressed. If you attempt to feed them while they are still adjusting, food will likely go uneaten and end up negatively impacting water quality. After 48 hours have passed, feed your new koi or goldfish a small amount of easily digestible food once daily. Limiting feeding will help prevent excess waste and ammonia build up.

Check water parameters, dissolved oxygen levels, and water temperature daily to ensure all are in an acceptable range. Because water quality is so important to the quarantine process, water changes are also essential. If your biological filter is established and working well, a 10-15% water change twice a week should suffice. Without an established biofilter, you should perform a 50% water change daily.

Salt should be added as needed to maintain 0.3% salinity. Not only does salt help reduce stress, but it can also act as the first line of defense against parasitic attacks.

If any signs of illness or disease are present, it’s important to quickly identify the issue and treat it immediately. Do not move any fish out of your quarantine tank and into your pond until any illness is thoroughly treated. Otherwise, you risk an outbreak in your entire pond, which can be difficult to resolve.

The End of Quarantine: Adding Fish To Your Pond

After 14 days, if no issues arise, you can add your new fish to your pond. It’s important to make sure that the water parameters of your pond are a near match to those of the quarantine tank. This will help make the transition less stressful for your new koi or goldfish.

To move fish from the quarantine tank, you’ll need to gently net each one and put them in a polyethylene fish bag filled with water from the quarantine tank. Gently submerge the net into the quarantine tank and try to coerce your fish into it. Exercise patience, as any abrupt or rapid movement with the net can cause unnecessary stress to your koi or goldfish. Once the fish is in the net, carefully remove it from the tank and transfer it to the fish bag. It’s common for fish to attempt escaping the net, so be sure to exercise caution when transferring.

When all fish are safely in the bag, close it with a rubber band and float it on the surface of the pond for about 20 minutes. Make sure the bag is not positioned within direct sunlight; cover with a towel or cloth if it is. After 20 minutes have passed, open the bag and release the fish into the pond. Again, avoid transferring any tank water to the pond.

It’s normal for koi and goldfish to be a bit timid when first added to a new pond. It’s not uncommon for them to hide or spend time at the bottom of the pond while adjusting. They may also appear to have a decreased appetite. These behaviors should improve as your koi or goldfish becomes more comfortable in its new environment.

Quarantining Sick Koi

Quarantine tanks can also be used to isolate and treat fish that are sick. There are several benefits to isolating a sick fish, including attempting to prevent the spread of illness to your entire pond population. While many diseases spread quickly, separating a fish as soon as it starts to exhibit signs of illness can help contain the impact.

Many of the medications used to treat koi and goldfish diseases are expensive, and they can be detrimental to your pond plants and water chemistry and negatively impact the filtration system. Treating fish in isolation allows you to avoid this. Quarantining sick koi also gives your fish the chance to recover in a less stressful environment. However, depending on the type of illness and how quickly it can spread, treating your entire pond may be necessary. Regardless, a water change should be performed for safe measure. You can find more information about symptoms and treatment procedures in our Comprehensive Guide to Koi Diseases and Comprehensive Guide to Goldfish Diseases.

When quarantining sick fish, the same basic procedures should be followed as when quarantining new fish. Do not add a canary fish when quarantining for illness. If you already know your koi or goldfish is sick, there is no need for this process, and doing so will unnecessarily expose your healthy fish to harmful pathogens.

Be sure to frequently monitor water parameters and perform routine water changes. Do not add a sick fish back into your pond until you are certain the underlying issues have been completely resolved. Your quarantine tank and equipment should be thoroughly cleaned after the fish is healthy and moved back to the pond to prevent the spread of illness when it is used again. This can be done using a mild bleach solution. Once the tank is sanitized, it’s a smart idea to get it back up and running so it’s ready for use when you need it again. Be sure that all traces of bleach are removed before setting up the tank again.

Before they are sent to your doorstep, all Next Day Koi fish go through a thorough health check to make sure they arrive in the best shape possible. However, the shipping process can be extremely stressful, which is why it’s important to take extra precautions to ensure your new koi and goldfish and your existing population remain in good health. The quarantine process is vital to accomplishing this. Of course, should any issues arise with your Next Day Koi fish during the quarantine period, they are covered by our industry-leading 14-Day Worry-Free Guarantee.

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