The practice of quarantining new aquarium arrivals, or sick tank-mates, is a crucial aspect of proper aquarium husbandry. Surprisingly, many aquarium hobbyists either neglect or decide not to quarantine new additions to the aquarium. Yet using quarantine tanks is crucial when introducing new aquarium additions or to prevent sick individuals from spreading diseases throughout the whole tank,

Any time you introduce a new marine species to your aquarium, there is always the potential to add harmful parasites or disease-causing species as well. Additionally, transport and relocation is very stressful for any species, which makes them more susceptible to succumbing to any disease or parasite they may be carrying. Therefore, this makes a quarantine tank a vital piece of equipment and a worthwhile investment to protect new and existing tank species.

Why Don’t All Aquarists Have Quarantine Tanks?

Most aquarists do not have a quarantine tank because of the perceived maintenance and the cost of an extra tank. However, a quarantine tank doesn’t have to be huge or costly, and it will likely end up paying for itself several times over. After you have gotten into the habit of using a quarantine tank, you will see the many benefits of this practice and never want to be without one again.

Why Are Quarantine Tanks Beneficial?

Parasites, injury, and infectious diseases are an unfortunate and unavoidable aspects of the aquarium hobby. The key benefit of a quarantine tank is to isolate your new fish (or invertebrates and coral) for observation. If there is any sign of parasites or an infectious disease, it is much easier to resolve as you can safely medicate the fish without risking the disease or parasite spreading to other members of your main tank. For new fish, a quarantine tank also allows them to become acclimated to new water parameters as well as a new diet in a safe, stress free environment. Additionally, it allows new tank-mates to recover from being transported, which is very stressful for them. 

When not in use as a quarantine tank, these tanks can even be doubled as treatment tanks. It is not good practice to medicate or treat the whole aquarium if you need to treat a problem that affects just a few fish. Whilst minimizing the potential spread of diseases or pests, quarantine tanks also serve other uses. Having an extra aquarium ready to use is great if one of your tank members is injured or if a fish is displaying aggressive behavior and needs to be removed temporarily from your display tank. Other uses for quarantine tanks include a breeding tank for fish, a recovery tank for harassed fish, or a “grow out” tank that allow newly hatched fry to mature in safety.

What Size Quarantine Tank Should I Use?

A quarantine tank between 10 and 20 gallons is a good size and is perfect for most freshwater and saltwater applications. However, a larger or smaller tank can work as well, and overall the size of the tank will depend on your needs. 

What Equipment Do I Need For My Quarantine Tank?

Most quarantine tanks have a basic setup with just the core essentials. This will include lighting, a heater, easy-to-clean rocks, and PVC tubes or plastic plants to provide some cover to help fish feel safe. For filtration, we recommend using a sponge filter as it works well, and the sponge can be colonized with nitrifying bacteria by placing it in the sump of your wet dry filter, or in the main display if a sump isn’t available. Make sure to disinfect and rinse your sponge filter well between uses. You do not need to add substrate and in fact can make cleaning and disinfecting your tank between uses very difficult. It is also a good idea to always have medicine on hand. Typically, you will need a general purpose medicine that can treat parasitic, fungal and bacterial pathogens. Specific medication is not needed unless a vet recommends it for your new additions.

In summary, a typical quarantine tank would have the following items:

  • A filtration unit
  • Heater
  • Powerhead
  • Test kits to check the pH, ammonia, nitrite, and nitrate properties of the water
  • Medication

How Do I Disinfect My Quarantine Tank?

The best way to disinfect the quarantine tank and any equipment between uses is with a mild (2-5%) bleach solution. Be careful to ensure that all traces of bleach are rinsed off before using the tank again. As an added precaution, a chlorine neutralizer is a good back-up to make sure you have effectively removed any potential chlorine residue. Drying also kills many but not all aquatic pathogens. Siphons are difficult to clean thoroughly, so it is easier to have a separate siphon for your quarantine tank that you can disinfect well between uses.

Quarantining New Fish

Any new addition needs to be slowly acclimatized to the water in the quarantine tank. There are a couple of methods you can use to do this safely, which you can read in more detail here. Once acclimatized, you should monitor the fish closely for at least two to three weeks for parasites and infections. Make sure to perform a 10-15% water change every other day to keep the inhabitants of the quarantine tank healthy. If there is any indication of a problem, use the necessary medication and keep the fish in quarantine for a few more weeks, consult a vet if necessary. Only when you are confident that the fish is happy and healthy can you then transfer them to your main tank for acclimatization.

Quarantining Sick Fish

When a fish in your main tanks becomes ill, it is the best just to net it and put it into the quarantine tank. If you use the water from your main tank then this will save you having to acclimate them. We do not recommend diagnosing the problem yourself as this can lead to making the problem worse. Instead, contact a local vet specializing in aquarium fish to diagnose the issue and advise you on the best treatment. Hopefully, after the animal has recovered from the disease you may still want to keep the fish in quarantine for a further week to continually monitor their condition. 

Quarantining New Coral

Quarantining can also extend to your new or existing corals too. New coral frags can carry a multitude of potential pests. Using a quarantine tank will help localize any outbreaks that may engulf an entire tank (such as Aiptasia) to help a pest and disease-free tank. For example, Acropora-eating flatworms, nudibranchs, or gorilla crabs are considerably easier to control in a quarantine tank rather than in your full display tank. Coral quarantine may even help prevent certain algae from entering your system.

We recommend setting up your quarantine tank like a normal trag tank with a bare bottom and keeping most of the live rock in the sump. If you do not quarantine your corals, especially very large tanks that are hundreds of gallons, it may become impossible to ever eradicate certain pests.


The value of a quarantine tank is clear, and it is important for every aquarist to have a quarantine tank. Controlling diseases and parasites is one of the most important aspects of this hobby, and as is so often the case, prevention is often better than cure.