The Freshwater Quarantine Tank

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Highly useful for isolating and observing new or sick fish, learn about QT basics.

This article was contributed by Aquarium Advice member Alivymar

The Quarantine Tank (aka QT tank) is one of the most useful and important pieces of aquaria equipment. It provides a place to keep new fish, to observe them for signs of disease prior to adding them to the main tank. It provides a place to isolate ill fish, to reduce stress from aggressive tank mates. Finally, it provides a place to treat ill fish without subjecting other fish and the nitrifying bacteria in the main tank to unnecessary medication.

There isn’t much needed; a container, a filter, aeration and a heater are the necessities.

Container : Depending on the size of the fish, a 5-10 gallon container is usually the easiest to work with. Notice I said container, and not fish tank. Why? Because a fish tank isn’t necessary as long as the container used is clean and safe. Many folk use Rubbermaid containers, purchased new and rinsed out well. Do be sure to buy one that is not treated to be mildew resistant (it will usually say it somewhere on the packaging). If you are more comfortable with a proper fish tank, a 10g tank can usually be found for around $10 USD.

Filtration and Aeration : A basic filter is all that’s needed. Nothing special, just one which will remove detritus from the water column. A HOB and a sponge filter are equally useful. Do keep in mind, if one uses a HOB filter, additional aeration is usually unnecessary as the HOB will agitate the surface adequately. If a sponge filter is used, additional aeration is required. Also, if the HOB filter media comes with carbon, the carbon will need to be removed if one is treating sick fish with medication.

Heater : Do purchase a dependable heater; fluctuations in temperature can be very stressful for the fish and contribute to problems.

Other Options : Some fish require hiding places for security. A plastic plant and/or a ceramic or plastic log will provide security as well as be easy to sterilize once one is finished with the tank. Gravel is an unnecessary addition, and can be difficult to sterilize. Also, if one is treating for ich, the cysts can hide themselves in the substrate making treatment a little more difficult.

Keep the Tank Up? Or Tear Down? There are a couple of schools of thought on this one; I feel the tank should be torn down between uses. Why? A number of reasons:

It’s a good idea to clean it out well and sterilize after returning/adding the fish to the main tank, especially if the fish have been treated for disease. One can sterilize the tank by adding bleach in a 9 to 1 ratio (9 parts water, 1 part bleach) and letting it run through the tank and filter for an hour or so. Rinse everything out well with fresh water, then rinse one last time with a triple dose of dechlorinator added to the water (which will remove any last remaining chlorine left by the bleach)

If one uses live fish to keep the QT cycled, there needs to be a place for them to live while the new or ill fish are in the QT tank. I buy new fish fairly often; the thought of dragging QT tank fish back and forth from tank to tank just doesn’t seem fair to me.

What about the cycle and ammonia/nitrites you ask? Many folks will keep extra filter media in the main tanks filter so it can be colonized by nitrifying bacteria, and use that in the QT tanks filter when needed. Instantly cycled tank! However, if the tank has been used to treat ill fish, any nitrifying bacteria in the filter have likely been destroyed. Therefore, even if the tank has had a mature bacterial colony, chances are it will have been killed off by the meds and the tank will start cycling from scratch again.

All in all, I see no reason to keep a tank up and running all the time. I want to be able to enjoy my tanks, and an empty tank serves no purpose IMHO.

Some Last Thoughts: Quarantining new fish can literally be a lifesaver; by keeping new fish isolated from the established tank for a period of time and observing them carefully, one can prevent the addition of stressful and deadly diseases to the fish currently inhabiting the main tank. By having a place to put ill fish, one can treat them without needing to treat healthy fish as well, plus reduce the healthy fish’s chances of becoming ill.

Some folks QT for 2 weeks; others for 6-8 weeks. Personally I quarantine wild caught fish for at least 3 weeks, domestic bred fish for 2 weeks (wild caught fish often come in with parasites which may not be obvious for a few weeks). However, the longer the QT period, the better the chance of the fish being healthy prior to addition to the main tank.

Keep in mind, the suggested time period for quarantine is variable; the addition of a new fish in the middle of a quarantine period means the quarantine period starts over again for all the fish in the QT tank. If one needs to treat for disease, the quarantine period starts over once the fish have been treated, to be sure they do not bring anything into the main tank. This goes for new fish as well as fish being treated for disease.

The Freshwater Quarantine Tank


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