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The Importance of Having a Quarantine Aquarium

Whenever thinking of adding new fish to an established aquarium, you should first look into setting up a quarantine aquarium. Think of it as an insurance policy. Although the local fish store may seem reputable, there really isn’t a 100% guarantee the fish you buy isn’t harboring some parasite or infection. It is always best to quarantine these fish first to avoid introducing disease. After all, there is nothing worse than having a happy, thriving aquarium for months or years suddenly start dying off because you bought a fish on a whim and added it directly to that setup. It’s an easy mistake to make, but it’s even easier to remedy by simply having a quarantine aquarium.

What is a Quarantine Aquarium?

A quarantine aquarium is any aquarium meant to house new livestock for a period of time to monitor for illnesses. It can also be used to isolate fish from an established aquarium that are injured, skinny, or otherwise in distress until they are nursed back to health. This setup is often bare bottom and therefore easy to sterilize between uses. It must include filtration and a heater to keep the water clean and at the right temperature. Any filters incorporated into a quarantine aquarium should exclude carbon as this will neutralize any medications added to the water. However, carbon may be added after treatments are complete to absorb any residual medication. Ideally, any other decor or objects in the aquarium should be easy to disinfect. This means live plants and driftwood should be avoided unless one is willing to throw them out and replace between uses. Usually a few fake plants and some sort of cave for the fish to hide in will suffice.

Where to Put a Quarantine Aquarium?

Whenever possible, a quarantine aquarium should be placed in a quiet room so new fish won’t be spooked as easily. They may be quite stressed out after traveling around the world from a wholesaler to a pet shop and then to you. It should be an aquarium that is appropriately sized for your new fish short-term. A ten gallon aquarium is a good size for quarantining most small/medium community fish. Like any aquarium, making sure the surface or stand for the quarantine setup is level and adequately supported is paramount to avoid leaks and other disasters.

How to Set Up

Once you’ve found the perfect spot for your quarantine aquarium, then it’s simply a matter of setting it up. The best way to get a quarantine aquarium going is to add filter media from an existing aquarium or by using a cycled sponge filter. This will instantly cycle the aquarium and allow you to add fish much sooner. It is always best to set up the aquarium a few days or even a week in advance of purchasing new fish to make sure the heater is working properly and that the aquarium is stable.

With that in mind, follow these steps:

  1. Make sure stand or surface to support aquarium is level and place empty aquarium on top
  2. Fill aquarium with dechlorinated water
  3. Place the heater in the aquarium and set to appropriate temperature (usually 76-82 degrees fahrenheit) before plugging in; add a thermometer to the side of the aquarium opposite the heater. This ensures accurate readings
  4. Set up external and/or internal filters, leaving out any carbon. Often a combination of an external power filter and internal sponge filter is ideal. If using a sponge filter, make sure the air pump supporting it is either above water level or has a check valve in place to avoid back siphoning during power outages
  5. Add any decor- a few caves/hiding places and fake plants are usually all that is required to make the fish feel at home for a few weeks
  6. Add a lid to keep evaporation down and prevent fish jumping out of aquarium
  7. Add established filter media or sponge
  8. Let run for 1-2 days minimum to make sure the heater and filter are running properly
  9. As long as the water tests out good (either run a water test yourself or take it to a local store to be tested), it is now safe to acclimate new fish to your quarantine aquarium

How Long to Quarantine?

Generally, anywhere from two weeks to a month is acceptable to quarantine a fish. Most diseases will present themselves in that time. After 2-4 weeks of monitoring, if the fish is still healthy you can acclimate them to the established tank. It may take longer than a month to pass through quarantine if the fish or fishes develop a nasty infection, although this is rare. It may also take longer than 2-4 weeks if you’re trying to nurse a fish from your established tank back to health in isolation. Treatment will ultimately depend on what symptoms your fish display. See our blog on Treatment of Common Aquarium Diseases to look into treatment options if fish get sick while in quarantine. 


If the fish do not display any symptoms of disease, simply feed your quarantined fish as normal and perform a water change of 25% once a week until 2-4 weeks have passed. If treating the fish, water changes of 25% should be performed daily followed by redosing medication for the duration of disease treatment. If using salt, only redose for the volume of water you are replacing (this will keep salinity from climbing). It is best to sterilize the quarantine aquarium and decor in a mild bleach solution after use, especially in the event that a disease outbreak took place and was treated or in the event that the fish died. Let everything completely dry before setting up again. Adding dechlorinator will ensure any leftover chlorine is neutralized. Sponges should be rinsed thoroughly and dried out between uses. Adding a dry sponge back to the main aquarium to re-seed with bacteria or alternating sponges (you can purchase extras) is best in preparation for setting up your quarantine aquarium again. If using a power filter, as long as a few weeks to a month have passed since you last used filter media from your established aquarium (and replaced it with new media), you can take this newer media and start the cycle all over again for your next fish acquisitions. 


Having a quarantine aquarium is instrumental in maintaining any display aquarium long-term. It can help you catch diseases in new fish and deal with them without compromising your entire collection of animals. It can also be useful in a pinch to isolate and save injured or otherwise compromised fish. If you can find the space for even one extra ten gallon aquarium, you can save yourself a lot of possible heartache. If you give it a try, I think you will find it’s an important and worthwhile investment.

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