Is It Okay to Quarantine Multiple Marine Fish at Once?

Sometimes QTing multiple saltwater fish in the same tank makes sense, other times it doesn't

Sometimes QTing multiple saltwater fish in the same tank makes sense, other times it doesn’t

As regular Saltwater Smarts visitors are well aware, “Caribbean Chris” and I are strong proponents of quarantining all newly acquired fish for at least four weeks before introducing them to a display tank. But what about keeping two or more fish in the same quarantine tank (QT) simultaneously? Is that an acceptable practice?

The answer to this question, as with so many aspects of marine aquarium keeping, depends on a variety of factors. Before proceeding with multiple-specimen quarantine, ask yourself these questions:

Am I doing this just to save time in stocking a new tank?

When contemplating the necessarily drawn-out process of quarantining all the livestock for a new display system, it might be tempting to think, “Hmm, if I just put all the specimens into quarantine at once, I can have a lively show tank in no time!” But this ignores the fact that whether you put all the specimens into the QT or display tank simultaneously, one sick fish among them will still infect the rest.

You also have to consider that the biological filtration in both systems will be tenuous at best at this stage. Adding too many fish to either tank at once will overwhelm the biofilter, causing an ammonia spike and potentially the death of specimens.

Were all the specimens sharing the same system water?

If the newly acquired specimens were purchased from the same sales tank or centralized system, then they’ve already been collectively exposed to any pests or pathogens that might have been present, in which case there’s no reason they can’t be quarantined together. I did this very thing last fall with a pair of bluechin triggers and a onespot foxface that were housed together at my LFS (all were good choices for my 125-gallon).

But again, you must always consider whether adding all the specimens to your QT or display tank at once is advisable given the potential impact on the system’s biofilter.

Do the fish vary in their tolerance of medications?

Keep in mind that if disease does rear its ugly head among your quarantined specimens, they’ll all need to be treated together. However, some fish tolerate certain protocols or medications (such as copper for treating marine ich) better or worse than others. Before quarantining different species together, do some research to determine how sensitive they are and what treatments/doses they’ll tolerate.

Is it necessary to add all the specimens to my display tank simultaneously?

Let’s imagine that, for some odd reason, you’re “Caribbean Chris” and you feel a strange compulsion to add a group of chalk bass to your display tank. After growing your beard and donning your spectacles, you head to the local fish store to acquire a group of five.

Now, when keeping chalk bass in groups, all the specimens should be introduced simultaneously, so it’s not really feasible to put each member of the group through quarantine individually. Nor is it practical to set up five separate quarantine tanks to house all the specimens. So in this type of situation, the most logical choice is to quarantine all of them at once in the same tank—provided you can answer “yes” to this last question:

Is my QT big enough to accommodate multiple specimens?

Of course, when quarantining multiple fish simultaneously, the QT itself must be large enough to allow adequate swimming space for all the specimens, provide enough hiding places so individuals can retreat from one another and feel secure, and sufficiently dilute the specimens’ combined waste products. After all, the point of quarantine is not to add stress on top of stress.


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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.

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