Adding A New Goldfish – The importance of “Isolate first, Socialize later”

Keeping goldfish can be an addiction. Seriously… it can.

After you have figured out how to keep them alive, you will begin to enjoy seeing them swim around in your fish tank. Your mind will start to give you reasons for adding a new goldfish to your tank. Hopefully before you succumbed to getting any more goldfish, you have already considered the necessary factors.

Adding A New Goldfish

So out you go looking for the next beautiful fish. When you got one, you just couldn’t wait to put it together with the rest of your fish family.  STOP! Do not do that yet!

Isolate first, Socialize later

Aside from birth defects, the main cause of goldfish’s problems is stress. Yes, stress… just like you and me.  Stress brings down their immune system and makes them vulnerable to diseases… again, just like you and me.

When you get a new goldfish, the process of catching it, bagging it and transporting it is stressful for the fish. For all that you know, the goldfish may have also been subjected to bad handling and living environment, contributing to its high level of stress.

So even when the fish is not showing any signs of disease at the time when you got it, it may already be infected. So there is always this risk of introducing a new pathogen, bacteria or virus into your healthy tank by adding a new goldfish that is infected.

That is why it is important to “Isolate first, Socialize later”. You should put your new goldfish into quarantine before adding it into the main tank.


Note: The following contains affiliate links. For more information, please visit my disclosure page.

What is a Quarantine Tank?

Apart from the main fish tank, every fish keeper should have a separate tank that serves as a quarantine tank. A quarantine tank is used for the following purposes:

  • As a temporary home for a new goldfish where it will be monitored or treated for any signs of infections before it joins the main fish tank.
  • As a treatment space for your sick goldfish. With that, you do not need to treat the whole main tank when not all of them are sick. Isolating the sick ones will also reduce the risk of them infecting the other fish.

A quarantine tank should not be too small and can hold at least 10 gallons of water. Of course, the bigger the better. With smaller quarantine tank, you will need to do more frequent water changes.

Tetra Aquarium Kit
A 29 gallons tank. Click to buy.

A quarantine tank should also be cycled.  You can do this quickly by using some of the filter media from your established fish tank. You will need to have a filter in a quarantine tank as well, and a simple inexpensive sponge filter is good enough.

You don’t need to decorate your quarantine tank as it is just a temporary place for your goldfish, but if you are into that.. why not? Knock yourself out.

Storage Container

If having a separate fish tank as a quarantine tank is out of the question, any containers that can hold a large volume of water will do, such as those plastic storage ones or tubs. It may be a bit difficult to view the fish from the side though.

How to quarantine a new goldfish?

Ideally you should already have a cycled quarantine tank ready when you bring a new goldfish home. It is also recommended to add aquarium salt or antibacterial medication into the quarantine tank as these will help the fish to calm down and build the immune system.

I am using this antibacterial medication called API MELAFIX Freshwater Fish Bacterial Infection Remedy for this purpose.


So how do you quarantine your new fish?

  1. When you bring your new goldfish home, float the bag (with your new goldfish in it) in the quarantine tank water for at least 15 minutes. This is to acclimate your fish to the quarantine tank’s temperature.
  2. After that, remove the new goldfish from the bag and put it slowly into the quarantine tank. Note: Do not pour the water from the bag into the tank as you do not want to contaminate your tank.
  3. Keep your fish in the quarantine tank for at least 2 weeks and monitor it for any signs of diseases. Also, please monitor the water condition as well and make frequent water changes. If there are signs of diseases, you will need to treat it accordingly.
  4. If after being in the quarantine tank for 2 weeks or more and the new goldfish is not showing any unhealthy signs, it is now ready to mingle and you can add it into your main fish tank!


As a goldfish enthusiast, building a healthy goldfish family is indeed a very exciting and addictive experience. When you already have an established fish tank, you want to make sure that it continues to provide a safe haven for your goldfish, and that is mostly within your control.

However when you are adding a new goldfish member into this safe haven, you may be introducing a new threat… and that threat comes in the form of a new pathogen, bacteria or virus. Are you willing to take this risk? A new infection can easily wipe out the whole goldfish family if it is not managed properly.

That is why it is necessary to quarantine the newcomers before introducing them to your main fish tank. So next time before adding a new goldfish, remember this yah – “Isolate first, Socialize later”

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6 Replies to “Adding A New Goldfish – The importance of “Isolate first, Socialize later”

  1. This is a topic i never would have thought about if i had not found your article. It was foolish for me to think of Goldfishes as simple-minded life forms and i never thought they could experience any level of stress.

    I am gearing up to start my own fish tank here in my house and want to avoid mistreating my fishes in any way.

    The quarantine tank is an excellent idea.

    If i purchase multi Goldfish at once is it safe to put them all into the main tank at once if they all came from the same handler?

    1. Hi Justin,
      Thanks for your comments. If you have other fish in your main tank, it is best to quarantine the new fish first. If there are not, then I think it shouldn’t be a problem to put them in.
      Anyhow I would suggest not to buy and add in many fish at one time as this may affect the water quality. The beneficial nitrifying bacteria need some time to adjust to the sudden increase of bioload.

  2. Whenever I go to the dentist, I will sit and watch the goldfish in the big aquarium that is there. I would watch those fish until the dentist is ready to see me. There must be something therapeutic about watching goldfish. I guess it helps to calm the fear of seeing the dentist.

    I have just learned a lot about keeping goldfish alive. I didn’t even know that their main problem could be stress, more so to keep them in quarantine. Now I have an understanding as to why my kids always lose their goldfish. I had no clue how to properly care for them. Thanks for sharing all the tips.

  3. I always thought, and the pet store clerks have told me the same thing. That all I needed to do was let the bag with the water and fish inside, sit in the tank so the water is equalized and the fish can then be added with no stress. I have done this many times only to have the fish die. Now I see that need to actually isolate the fish first. I have learned some valuable information here! Thank you!

    1. Hi! Yeah, it is very advisable to quarantine the new fish just to make sure it doesn’t carry with it any disease. This is to protect the other fish that you already have in your tank.

      Thanks for the comment!

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