While this article by Taro Kodama is a bit commercial in terms of recommending their own products, it does have very good info, and is worth the read!  I did not include, but they do sell, a complete Q tank kit and a complete accessory kit – the both contain a good group of items.

Koi Health Awareness: Quarantining Koi

It is our goal to see your koi thriving! It is essential you are comfortable with quarantine procedures, so that when you receive new Koi, they are healthy!

It's a sad thing to see a Koi sick, especially if it's been your friend for a long time. Sometimes the cause is a mystery and can keep you up at night.

You have probably heard the phrase “Location, location, location”, often quoted by real estate agents. 

In the Koi world, we say “Quarantine, quarantine, quarantine. This should be rule #1, but it is often the most overlooked by Koi owners...

It is critical to quarantine any new Koi from other ponds because the newly purchased Koi may carry parasites, bacteria, fungi, or viruses. 

Your Koi providers, whether you buy Koi from your friends or a store, did their best to eliminate them; but unfortunately all it takes is an unhatched egg to break out in your main pond and make all your other Koi sick.

In our new article, we will cover these essential koi quarantine questions:

• Why do I need to quarantine Koi?
• What might happen if I do not quarantine?
• How do I setup a Koi quarantine tank?
• What are important tips for Koi quarantine procedures?
• What are your recommended Koi quarantining products?

Why is it so important to quarantine new Koi in a tank?

Imagine you just got a beautiful new Koi.

You are excited to see and feed the new Koi in your pond.

But wait!

Do not introduce the new Koi to your pond yet. Keep the new Koi in a separate tank and monitor it for several weeks.

It is critical to quarantine any new Koi from other ponds because the newly purchased Koi may carry parasites, bacteria, fungi, or viruses.

Your Koi providers, whether you buy Koi from your friends or a store, did their best to eliminate them; but all it takes is to overlook an unhatched egg of a parasite, which is microscopic. You do not want it to break out in your main pond and make all your other Koi sick.

Even if if a new Koi is all clean and healthy, it is often exhausted and stressed from the journey to your home, especially if it is shipped overnight from a dealer. It is usually weak from the trip and has low immunity. So if introduced to the main pond too soon, it could get infected from something that your other current Koi are already immune to.

In short, the purposes of quarantining are to:

1. protect your current Koi in the main pond
2. nurse the new Koi back to full health before it dives into your main pond

What might happen if I do not quarantine?

If you deal with a few dealers that you trust, most of the time, nothing may happen when you introduce a new Koi to your pond.

But 1 out of 100 purchases, a new Koi may come with an egg of a parasite in tow.

If it hatched in your main pond, your other Koi will feel itchy and start scratching themselves. If you catch the symptoms early enough, treating them is easy, but if you are late to react, it will worsen into a secondary bacterial infection from the scratching. And this new infection will spread to other Koi.

Whether a secondary infection or not, once infections spread, not only will it be more difficult to treat, but it may also damage your Koi’s beauty. The worst is if a Koi should happen to carry KHV (Koi Herpes Virus), you might potentially lose your whole collection of Koi.

I do not mean to scare you, but do want to inform you about the serious hazards to your pond without a protective quarantine process!

How To Setup Koi Quarantine Tank System

These quarantine items help protect your Koi from outside invaders and disease.

To set up a quarantine tank, see the illustration above showing a completed setup.

You can use the following lists to ensure your quarantine tank and accessories are complete.

Quarantine Essentials:

1. quarantine tank
2. water pump
3. tubing
4. filter
5. air pump
6. air tubing
7. air stones
8. pond cover net

Quarantine Accessories:

1. water thermometer
2. test kits for ammonia, ph, nitrite - and you should also have a KH test kit!
3. salt meter
4. salt
5. ChlorAmX (dechlorinator and ammonia binder)
6. Prazi
7. Ich-X
8. heater

5 Koi Quarantine Procedure Tips

As you can see by now, a good quarantine procedure is a life line in this hobby.

To fully enjoy the hobby, you need to learn how to play it safe.

Setting up a quarantine system is pretty simple. You can set up a temporary version without a filter or a more permanent version with filter system. Either version will do the job, but you need to keep the following in mind.

1. Check water parameters constantly

Quarantine tanks are usually much smaller than your regular ponds and therefore water parameters can change very quickly, especially if you use a temporary version with no filter. For a quarantine tank with no filter, I recommend you feed no or very little feeding. Feeding will increase ammonia and nitrite level and you will be forced to change water often. If you feed, keep it very light!

2. Manage water temperature

Keeping water temperature warm is another important quarantine tip.

Your Koi’s immune system works the best when water is over 70° F. At this temperature, they can more quickly recover from the stress and exhaustion of the journey to a new environment. It is also important because the most dangerous disease in Koi hobby, KHV (Koi Herpes Virus), appears only in warm water temperatures. And it takes about 2 weeks to break out if there is any.

3. Add a small Koi from your pond

This is also a good way to tell if the new addition to your pond may cause any issues.

If new Koi carry any bugs, it should affect this Koi. Or vise versa. Koi in your pond may carry something but already immune to it. If your new Koi are not immune to it, you will see the problem in the quarantine tank. So the Koi plays the role of a canary in coal mine. Plus, Koi are social animal. They always do better when they have companions. It will help new Koi adapt to the new environment.

If you set up a more permanent quarantine tank with filter, these canary Koi will keep your biological filter going.

4. Get advice, (but…)

This is not just in quarantine, but Koi hobby in general. If you observe something unusual, don’t panic.

First check all the water parameters such as water temp, ammonia, nitrite, pH. Then, pick up your phone and call your dealer for advice. You may have many dealers and friends to talk to, but at many times, listening to many and trying to do everything make the situation worse. Stick to a few experienced sources to keep advice consistent

5. Quarantining new Koi is your responsibility

As the owner of your beloved and beautiful Koi, it is your responsibility to quarantine new Koi and protect your precious collections.

Often, I am asked if it is OK to introduce new Koi direct to a pond. As a Koi dealer and also a Koi lover, I can not and should not say “Yes you can.” You should always quarantine new Koi. As a dealer of Japanese Koi, I do everything I can to provide clean and healthy Koi, but dealers including myself should not be over-trusted.

Again, it is only you who can protect your existing Koi and safely introduce a new family member to your pond.

How do you Quarantine New Koi into a Tank?

Once you receive a new Koi, please release it in a separate quarantine tank.

Then follow these abridged instructions:

1. Add 3 lb salt/100 gal water to your quarantine tank (0.3% salinity)
2. Observe the new Koi carefully to assure it does not develop disease for 14–21 days
3. If your quarantine tank has a filter, please feed the Koi lightly.
4. If your quarantine tank has no filter, you may still feed them lightly, but do a partial water change every 2–3 days (about 25%). Add salt to maintain 0.3% salinity.
5. After 3–5 days, if the Koi looks well, you may use Koi Prazi and Ich-X to deal with any potential parasites
6. Throughout the quarantine, check the pH, ammonia, and nitrite levels regularly
7. Maintain a water temperature of 65–78 F, ideally 70+ F.

THANK YOU Taro!   Source:  https://www.kodamakoifarm.com/koi-quarantine-tank-setup-procedure/