How To Introduce New Goldfish To A Tank

Getting a new goldfish is so exciting! 

You can’t wait to introduce your new fishy friend to his tank mates and watch him settle in, right? 

But you can’t simply put your goldfish into the tank and hope for the best! To give your new pet the best start in his new home, it’s crucial that you introduce him to his new environment correctly.

Read this guide to learn how to introduce a new goldfish to your fish tank.

Creating a quarantine tank

When you buy a fish from a fish store, you have no way of knowing where that fish has come from or what diseases or parasites the fish might be carrying.

Of course, you don’t want to accidentally bring problems into your fish tank with your new fish that could harm your existing pets. The best way to prevent that from happening is to put your new fish in a special quarantine tank first.

What is a quarantine tank?

A quarantine tank is simply a fish tank where new fish, invertebrates, and plants can be kept until you’re sure they’re healthy and don’t pose a risk to your existing livestock.

If your new fish shows signs of any disease while it’s in the quarantine tank, you can treat the problem until the fish has recovered.

You should set up the quarantine tank with the same water conditions and basic environment as your main display tank. That way, your new fish will feel right at home when you move him to join his tank mates.

How long do you have to wait to put goldfish in a new tank?

How long you need to wait before you can add your new goldfish to your tank depends on whether the tank has “cycled.”

Introducing fish to a new tank

If you have a brand new tank, you need to ensure that the tank is properly cycled before you introduce any fish to the environment.

Goldfish produce lots of waste. That waste gradually decomposes, releasing a chemical called ammonia. Ammonia is highly toxic to fish, and if the ammonia is not removed from the water by an efficient filtration system, your poor goldfish will quickly die!

So, what can you do to make the water safe for your fish?

The Nitrogen Cycle

Your filtration system works by passing all the water in your fish tank through the various filter media in the tank. 

The biological filter media contains colonies of beneficial bacteria that process the ammonia and turn it into nitrites. Nitrites are also dangerous to your fish. However, in the next stage of the process, more species of bacteria convert the nitrites into less harmful nitrates.

That process is called the “nitrogen cycle,” and you can read more about how the cycle works in our dedicated guide.

A new fish tank can take up to two months for the nitrogen cycle to be complete. Once the tank is “cycled,” it’s safe to add a couple of small goldfish. 

It will then take a few more weeks for the existing colonies of bacteria to be able to cope with that additional load. Then, you can safely add more fish to your collection.

How do I know when my new fish tank is cycled?

To check if your new tank is properly cycled, you need to test the water with an aquarium water testing kit.

The levels of ammonia and nitrites in the water must be zero, and the nitrates should be below 30ppm (parts per million).

Once that environment is achieved, it’s safe to add fish to the aquarium.

How do I get my goldfish ready for a fish tank?

Even if you have a new tank that’s cycled or an existing tank that’s already mature and ready to welcome new fish, you can’t just dump your new pet into the water!Before adding your new goldfish to your fish tank, you need to acclimate him.

Why do I need to acclimate fish?

Although goldfish are pretty hardy creatures, they are still sensitive to changes in their environment and to fluctuations in temperature and water parameters. If the conditions are unsuitable for the fish, your pets will quickly get stressed and sick.

When you buy your goldfish in a pet store, the conditions the fish have lived in will probably be slightly different from those in your home aquarium. For that reason, it’s crucial that you acclimate the fish properly when introducing him to his new home.

Properly acclimating your new goldfish ensures that your pet adjusts to the different water chemistry and temperature in the tank so that he doesn’t get stressed and sick.

How do I acclimate new goldfish to a tank?

There are two acclimation methods that most hobbyists use:

  • Float acclimation method
  • Drip acclimation method

The drip acclimation method is very slow and laborious, so we recommend that you use the flat acclimation method.

Make A Stress-Free Environment:

Before you begin to acclimate your goldfish, you need to create a stress-free environment for your pets.

Bright light can be highly stressful to your fish. If you keep the tank dark, you give the fish an opportunity to become oriented in their new habitat. So, start by turning out the aquarium lights to reduce stress on your new fish.

Wash Up!

Now, you need to wash your hands to remove any lotions or creams that might otherwise contaminate the water.

Float Acclimation Method

Now, you can begin to acclimate your new goldfish.

1. Temperature

Goldfish can tolerate a wide range of temperatures from 68° to 74° F. 

However, sudden fluctuations in temperature can be highly stressful to the fish. Ideally, the water temperature in the transport bag should be the same as that in your fish tank.

Adding the goldfish straight into the tank from the plastic transportation bag could plunge your pet into temperature shock, and that could be fatal!

So, you should float the sealed plastic bag in your aquarium for at least 15 minutes. That allows the temperature in the bag to equalise with that of the tank. 

Don’t float the bag for longer than one hour. After that time, the available oxygen in the bag will run out, and the fish waste could reach harmful levels.

2. Water Parameter Acclimation

When the bag has been floating in your tank for 15 minutes, cut the bag open with a pair of sharp scissors, as close to the top as you can.

Fold the edge of the bag down about an inch. That creates an air pocket inside the bag’s lip, which keeps the bag floating. If you’re afraid that the bag might sink, attach it to the side of your tank with a peg or algae clip.

3. Add Tank Water To The Bag

Take a cup of aquarium water and gradually add ¼ to ½ of the cup to the floating bag. Keep adding water every few minutes until the bag is full.

4. Tip Some Of The Water Out Of The Bag

Once the bag is full, take it out of the tank and tip away half the water into a bucket, taking care not to frighten your fish.

5. Float The Bag Again

Now, put the bag back into your tank. Add around ½ cup of water to the bag and repeat every two minutes or so until the bag is full.

That process further acclimates the fish and removes most of the old water that was still in the transportation bag.

6. Empty The Bag

Once the bag is full, remove it from the fish tank and slowly pour out as much of the water as possible into your bucket.

7. Introduce Your New Goldfish To The Tank!

Now, you’re ready to put your new goldfish into your tank!

Carefully, grab the bag by the bottom corner and very slowly lower it into the tank. Tip the bag to allow your new pet to swim out into the aquarium.

Tip any remaining water down the sink, not into your fish tank.

Why are my current fish being aggressive towards my new fish?

Goldfish are peaceful creatures that don’t generally show aggression toward each other or to other fish species in a community.

However, when a new fish arrives in the tank, there’s bound to be some curiosity among the existing crew!

You might find that your new fish receives rather a lot of attention from his new tank mates. That’s often the case if the newcomer is female and you have male fish. 

Juvenile males often chase a new female around the tank, and you might even see some spawning behaviour!

In my experience, things typically settle down within a few days once the fish get used to each other. Interestingly, goldfish in a pond tend not to exhibit that kind of behaviour, probably because they have more space and places to hide.

What to look out for with new goldfish in a tank

If you’ve kept your new goldfish in quarantine for a couple of weeks before introducing your fishy friend to your main tank, you shouldn’t have any problems.

However, there are a few things to watch out for when introducing a new fish to your aquarium.

Poor Water Quality

If your fish are hanging at the water surface, that’s often because the tank lacks dissolved oxygen, usually due to poor water quality.

Similarly, goldfish that sit immobile on the bottom of the tank, breathing rapidly, are usually affected by dirty water that contains high levels of toxins, typically nitrates.

Carry out a partial water change of at least 30%, and then test your aquarium water. If the levels of nitrate are above 30ppm, carry out another partial water change of 10%.

Make sure that your filter system is working properly and change the media if necessary.

Signs Of Sickness

Goldfish love being in a group of the same species. A fish that spends much of its time alone and away from its tank mates is not a happy fish and could be sick.

Goldfish are greedy creatures! If your fish is not eating or showing any interest in foraging for food, your pet could have an internal bacterial infection.

White Spot Disease

No matter how carefully you introduce your new goldfish to your existing tank, the situation is pretty stressful for your new pet. 

Stress can compromise the fish’s immune system, leaving the animal open to attack by parasites and diseases. One very common parasite that commonly affects new fish is Ichthyophthirius multifiliis, also called Ich, Ick, or White Spot Disease.

The Ich parasite initially causes the fish to flick or flash against solid objects in their environment. After a few days, the fish starts to display a rash of tiny white spots like grains of salt.

Luckily, Ich is pretty easy to treat and is rarely fatal.

Bacterial Infections

Bacterial infections are another common problem in new fish, again largely due to the effects of stress.

Bacterial infections can show up as red patches on the fish’s body, ripped fins, lethargy, and lack of appetite. Depending on the cause, you can usually treat minor bacterial problems with an appropriate over-the-counter medication that you’ll get in good pet stores.

Swim Bladder Problems

If you notice your new goldfish floating up to the surface, apparently unable to swim down again, swimming on one side, or even swimming upside down, it most likely has a swim bladder problem.

Fancy goldfish commonly suffer from swim bladder problems that are generally caused by constipation or bloat.

You can usually fix the problem by fasting your fish for a day or two, and then offering your pet some fresh veggies or frozen meaty food, such as bloodworms. That often does the trick within a few hours.

Prevent constipation by feeding your goldfish a varied diet that includes specially formulated Fancy goldfish pellets, fresh veggies, and frozen bloodworms and daphnia.

How can I tell if my goldfish are happy in their new tank?

Happy goldfish are generally pretty active creatures that spend most of their time foraging around the bottom of the tank for scraps of food or grazing on algae. 

Your goldfish should also be keen to feed when you approach the tank at feeding time. 

Final Thoughts

I hope you enjoyed our guide on how to introduce a new goldfish to a tank. If you did, please take a moment to share the article!

Before introducing a new goldfish to a new tank, ensure that the tank is properly cycled so that the water is safe for your pet. 

When putting a new goldfish into an existing tank, quarantine your new pet for a couple of weeks first to be sure he’s healthy and not bringing diseases with him that could affect your existing community.

In both cases, take the time to acclimate the newbie properly before putting him into the tank to avoid shocking your pet.

3 thoughts on “How To Introduce New Goldfish To A Tank”

    • Hi Melanie,
      yes you can, it is best to use drip acclimation for this, keep adding the tank water to the bag/container in small doses so the fish can get used to the softness of the new water

  1. I have glo fish and want to know once I clean the tank how long should I wait before replacing them back in the tank?


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