5 Myths About Marine Quarantine Tanks

A standard quarantine aquarium setup

A standard quarantine aquarium setup

Quarantine tanks are often discussed/written about as though they require very little effort, planning, or expense. Just dust off that 10-gallon plastic “critter keeper” sitting on the shelf, fill it with salt water, drop in a heater and sponge filter, and you’re good to go, right? Unfortunately, it’s not really that simple.

One could argue that in their justifiable zeal to encourage marine aquarium hobbyists to quarantine all their livestock, some aquarium authors (myself included, admittedly) and others with a voice in the hobby have created some false impressions about the practice. Here are a few of the quarantine tank myths I’ve noted over the years—and probably even perpetuated to some degree:

1. A 10-gallon tank will do ya!

This may be true for very small species, but many of the specimens swimming in the sales tanks at your LFS will be significantly stressed if crammed into such a small system for a minimum of four weeks (potentially even longer if disease treatment is necessary). I’ve found that a standard 29-gallon tank—which, let’s face it, will cost significantly more than that plastic keeper with the slotted lid—works pretty well for most of the specimens available in the trade.

It’s also important to remember that, just as with small display tanks, small quarantine tanks are less stable than larger ones with respect to water quality, chemistry, and temperature, which can add stress on top of stress for newly acquired specimens.

2. No substrate is necessary

Again, this is often the case, but not always. Burrowing or burying species, such as jawfishes, shrimp gobies, and various wrasses, often find the absence of substrate highly disconcerting. In fact, I once had a newly quarantined Wheeler’s shrimp goby (Amblyeleotris wheeleri) repeatedly slam itself against the glass bottom of the tank in an effort to reach anything resembling the ocean floor.

That doesn’t necessarily mean you need to have substrate covering the entire bottom of your quarantine tank. Oftentimes, fishes that burrow or bury themselves will be content with a tray filled with substrate material. Some may even do okay with sections of PVC pipe to hide in, but be ready to add at least a tray of substrate if PVC “caves” don’t cut it.

3. You don’t need lighting either

I would amend this to say you don’t need dedicated lighting for a quarantine tank. You do, however, need the ability to observe quarantined specimens clearly for signs of disease, and that’s kind of difficult under ambient lighting.

When I have a fish in quarantine, I don’t keep a light fixture permanently in place over the tank. Instead, once a day, I briefly transfer one of the LED fixtures from my adjacent 125-gallon FOWLR tank to the quarantine tank so I can give the specimen a good “once over,” then I move it back to the display tank. This process can be a bit of a hassle, but it doesn’t cost me anything.

4. Quarantine tanks are just for disease prevention

If you’re acquiring a specimen that you’re fairly confident isn’t diseased (e.g., from a trusted fellow hobbyist), you may be tempted to skip the quarantine stage because there’s no point to it. But remember, the quarantine period isn’t just a time to observe or treat for disease. It’s also an opportunity for new specimens to recover from transfer as well as get accustomed to your particular water conditions and the foods they will be offered before they have to compete with tankmates in a display system.

5. Biofiltration is unimportant

Advising hobbyists that a quarantine tank can be set up only when needed and taken down afterward may create the false impression that it doesn’t need to have a mature biofilter in place. Just as with a display aquarium, a quarantine tank must have biofiltration in place to convert deadly ammonia to less harmful compounds before it can safely hold any livestock.

Because quarantine systems tend to be temporary setups, biofiltration is usually provided by either borrowing live rocks from an established system or by using a sponge filter or other type of biofilter that has been operating on an established aquarium (in addition to the system’s primary filtration) and is, thus, already inoculated with beneficial nitrifying bacteria.


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About Jeff Kurtz

Jeff Kurtz is the Co-founder/Editor of Saltwater Smarts, former Senior Consulting Editor for Tropical Fish Hobbyist Magazine, and the aquarist formerly known as “The Salt Creep.” He has been an aquarium hobbyist for over 30 years and is an avid scuba diver.


  1. Paul Baldassano says

    I don’t use quarantine tanks as I do something different but on the rare occasions when I get a fish from a supplier that is very sick and I need a hospital tank to cure it, I just fill a tank with water from my reef tank and take some rocks from the reef to stock it with. Every day I remove and discard water from the hospital tank and replace it with water from my reef. I replace the reef water with new water. This also gives me the benefit of changing some water in my reef which should be done anyway. I would not filter water in a hospital tank or any tank where medications are used as that would remove the medications.
    I recently acquired some copperband butterflies for free that were so ich infected that they were about to die. I cured them in a few days and gave them away

  2. Matt Bowers (Muttley000) says

    I’m glad you included point #4, and would add it’s not only a chance for the fish to get used to your regimen, but also a time for you to get used to the fish and to observe it’s habits.

  3. The first four points are very valid. The last point is a moot one of you’re medicating the fish in the hospital tank. Most likely, the medication, especially copper being used to medicated for ich, will kill every last bit of bacteria in the water anyway.

    As for the comment of changing water from the reef tank to the hospital tank, this is a terrible idea that will lead to reinfestation of your fish with whatever you’re quarantining your fish from in the first place and assures your fish not recovering from whatever disease they had in the display tank, such as ich, marine velvet, etc.

    • Jeff Kurtz says

      Hi John! I should have emphasized that this post is generally referring to quarantining newly acquired specimens before they’re introduced to the display tank, so using live rock or a sponge filter from the DT for biofiltration (or transferring water from the reef to the QT per Paul B’s comment above) should present no risk of transferring disease to the quarantine system. And true enough, if the specimen proves to be diseased and you do need to medicate the quarantine tank, loss of biofiltration may be an issue you’ll have to contend with.

      • Yes, true enough. I didn’t realize that it was referring to initial quarantining.

        • Jeff Kurtz says

          Totally my fault there! The idea was in my head but it didn’t really come across in the post.

          • Leon Conrad Neill says

            So, when medicating for ich in a QT, you have no other option than to do big water changes every day? and if so, what is the recommended percent to take change?

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