When Should I Set Up a Quarantine Tank for My Fish?

by Britt
Photo credit: Theera Disayarat / Shutterstock.com

If you are new to fishkeeping, you have likely noticed that there is a lot more involved in setting up a healthy, thriving aquarium than most people realize! From the ideal tank setup to managing water levels, there is much to learn – including the basics of fish health. One topic that is often overlooked but can be incredibly important in terms of your tank health is the use of a quarantine tank.

But what is a quarantine tank, and when should it be used?

In this post, we will look at how a quarantine tank can improve the overall health of your existing aquarium, including how to set up, maintain, and disinfect your quarantine fish tank.

What is a Quarantine Tank?

Before we dig into the finer details, let’s start at the beginning – what is a quarantine tank? Quarantine fish tanks are smaller tanks set up to help limit the potential spread of illness or disease. They do this by effectively quarantining the sick (or potentially sick) fish separate from the main tank or aquarium.

Think of the tank like a human hospital. If a person is suspected of possibly having an infectious disease, steps are taken to prevent that disease from spreading to anyone else. This includes removing the person from the general public, limiting access to them, and maintaining a clean and sterile environment.

In the same way, your quarantine tank isn’t going to be set up as a fancy, decorative area. Instead, the focus is put on eliminating anything that could increase the transmission of disease. For this reason, they are often free from decorations and aquarium gravel or other forms of substrate. This allows you to create a clean and stress-free area for your fish – especially if they are being treated for or recovering from an illness.

When Should I Put My Fish in a Quarantine Tank?

A quarantine tank setup can serve several different purposes in your fishkeeping efforts. This includes everything from safely introducing new fish to the aquarium to treating any illnesses that may arise. The good news is that you only have to invest once in all this equipment and keep it disinfected between use, and it will serve you well time and time again. Here are a few of the most common uses for a quarantine fish tank:

Bringing Home New Fish

Anytime that you bring new fish into your home, there is a risk that you are also bringing illness or disease with them. This is especially true if you have purchased fish from a larger pet store where large quantities are kept in a tank display. Not only does this allow you to monitor the fish for signs of illness, but it also provides the opportunity to properly acclimatize the new fish by slowly introducing water from the main fish tank. This will allow them to adjust to the specifics of your tank setup, including nutrient levels, pH levels, temperature, oxygen content, and more.

The length of time necessary for quarantine and the acclimation process is unclear. Some experts say the process can be done in as little as 15 to 60 minutes. However, others argue that this doesn’t provide enough time for any potential illnesses to be ruled out. Experts may recommend as much as 2 to 4 weeks to ensure that your new fish are healthy and don’t pose a risk to your existing tank setup.

Hospital/Treatment Tank

Another excellent use for your quarantine tank is the treatment of any existing fish that may be showing signs of illness. At the first sign that there may be something wrong with a fish, remove them from the tank in an effort to limit spread. An in-depth tank cleaning should follow this to remove any potential dangers.

Not only does a standard quarantine tank setup help to reduce the spread of illness by quarantining the fish and removing any areas where infectious bacteria could be hiding (like in aquarium gravel), but it’s also the ideal setup for administering medication to help your sick fish overcome their illness. Your ill fish should be kept in the quarantine tank throughout the complete medication cycle and for 4 to 6 weeks following the last disease symptom to ensure that they have fully recovered.

Address Bullying/Harassment

You may encounter a situation where a new fish is bullied or picked on by the existing fish in your aquarium setup. This can result in injuries to the bullied fish, like fin damage that can negatively affect their ability to survive the ordeal. When this happens, it is recommended that the injured fish be removed from the tank and given time to recover safely. Your quarantine tank is a great option for this recovery phase.

When introducing a bullied fish back to the main tank, there are steps you can take to address the behavior and boost your chances of success. This includes:

  • Ensure your tank is large enough. The general rule of thumb is one gallon of water per one inch of fish, but many experts say even more space is ideal.
  • Provide plenty of hiding spaces around the tank for the bullied fish to retreat if needed.
  • Research to ensure that the species of fish you are keeping can survive together peacefully. If not, you may need to consider a secondary tank setup to keep certain species separated.
  • Consider adding one or two more of the species of your bullied fish if they are the only of their kind. This can help to balance numbers and create a better balance in the tank.

Most importantly, make sure that you are carefully monitoring your tank after reintroducing the fish, watching for any signs that bullying and harassment are continuing to happen. Just as not all people get along, the same can be said for our fish. There is always the possibility that your fish simply can’t peacefully coexist. At that point, you must consider setting up another tank or rehoming one of the fish.

Breeding or Nursery Tank Needs

Are you considering getting into breeding as part of your fishkeeping journey? If so, a few options exist to keep the fry (baby fish) safe. While breeder boxes can be introduced to your main tank to try to contain the fry and keep them protected, many fish keepers will instead use a separate breeding or nursery tank. This eliminates any issues between the fry and the other adults in the main tank.

Before repurposing your quarantine tank as a breeding tank, you must ensure that it is large enough to support the needs of the parents and their fry. If the tank is too small, you significantly reduce their chance of survival.

Photo credit: Theera Disayarat / Shutterstock.com

How to Set Up a Quarantine Tank

Now that we have established why you should consider setting up a quarantine tank, let’s break down the steps required to do so correctly. After all, your tank’s overall setup could significantly impact its effectiveness in containing and eliminating infectious diseases in your fish.

Step 1: Selecting the Right Tank

The ideal quarantine tank size will vary depending on your planned uses for the tank and the species of fish you are keeping. For example, larger fish will need a larger tank. At the same time, even if your fish are smaller but you plan on using the tank regularly as a breeding tank, you may want to opt for a larger size.

Here are a few recommended sizes to use as a starting point when making your decision:

  • Betta: 2.5 to 5 gallons
  • Goldfish 20 to 30 gallons
  • Cichlids: 20 to 50 gallons
  • Marine fish: 10 to 100 gallons

Select a tank with a tight-fitting lid to keep your fish safely contained, especially if you have fish prone to jumping.

Step 2: Disinfect the Tank Before Each Use

Each time you go to use your tank, take a moment to clean and disinfect it. This is in addition to disinfecting the tank following use. Just as we take extra precautions to keep a sanitized environment in human hospitals, the same should be done for your “fish hospital.”

How do you disinfect a quarantine tank? You can sterilize your tank using either a bleach/water solution (9 parts water to 1 part bleach) or a vinegar/water solution (1 part water to 1 part vinegar). This should not be used with any other cleaning chemicals, or you run the risk of negative interactions. As this is a bare-bottom tank without the use of decorations, you won’t have to concern yourself with cleaning these other elements.

Step 3: Add Necessary Equipment

Lighting is generally not needed for a quarantine tank. In fact, lighting can have a negative impact on some medications, reducing their effectiveness. You may wish to add a simple light that will allow you to check on the fish and look for signs of infection or parasites, but this isn’t going to be the most critical area to invest your hard-earned money when creating the ideal quarantine tank.

Heating and filtration are essential as they will create the best possible healing environment. Use a heater that allows for complete heat control versus a preset heater, making it easier for you to reach the ideal temperature. For filtration, a sponge filter is the best option. This allows for beneficial bacteria while minimizing water flow.

Step 4: Offer a Sterile Hiding Space

We already established that decorations can be detrimental to a quarantine setup. They often contain small divots and spaces where bacteria can hide and grow, worsening an existing situation. However, most fish need a safe hiding place to feel safe and secure in their environment.

One effective solution is to use a small piece of PVC pipe. The pipe has a smooth surface, meaning there are no spaces for bacteria to hide. Unlike most commercially available tank decorations, it can easily be cleaned and disinfected when you are done.

Step 5: Add Water

When adding water to your quarantine tank, use about 50-75% fresh water. The rest should be water from your main aquarium. This will allow you to introduce the parameters of your main water setup that your fish is already used to. This reduces the stress and complications that can come from sudden changes in the water your fish is living in. Make sure to test the water before putting your fish in the tank.

Step 6: Proper Acclimation

Even with the consideration for including your main tank water in the quarantine tank, you will still need to take time to properly acclimate your fish to the new tank setup. Just as you would slowly add in the water for your main tank to the water a new fish arrived in, you should do the same with the fish you are moving into your aquarium tank. This will give them time to adjust to the water in the tank without any added stress. After all, stress can increase the risk that your fish will succumb to disease.

Final Thoughts: Using a Quarantine Tank for Your Fish

A quarantine tank is an effective tool for protecting your main aquarium and controlling the potential spread of disease. This includes reducing the risk that new fish will bring disease and illness into your tank, as well as addressing any infections that may arise within your current fish population. But for the tank to fully serve its purpose, it must be set up correctly.

A functional quarantine tank will be clean and sterile to fight the spread of disease. To do this, you should avoid using tank decorations or substrate. A bare-bottom tank creates an environment with as few spaces for bacteria or parasites to hide, grow, and spread as possible.

Of course, quarantining the sick fish is only one part of the equation. In addition to separating the ill fish from the rest of your fish population, you must also focus on properly cleaning your main aquarium to remove contaminants.

The best thing you can do as a fish keeper is to regularly monitor your aquarium for any signs of trouble. The sooner you recognize the signs of illness in your tank and take action, the greater the chance you will be able to control the spread and prevent the situation from getting significantly worse.


Britt Kascjak is a proud pet mom, sharing her heart (and her home) with her “pack” which includes her husband John, their 2 dogs – Lucifer and Willow – and their 2 cats – Pippen and Jinx. She has been active in the animal rescue community for over 15 years, volunteering, fostering and advocating for organizations across Canada and the US. In her free time, she enjoys traveling around the country camping, hiking, and canoeing with her pets.

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