Why quarantine?

Quarantining fish is one of the best ways of avoiding the introduction of parasites and diseases into the display tank. It also provides a good environment for new fish to adjust to life in captivity and learn to eat prepared foods away from competition from other fish.

See Quarantining Your Fish for a discussion on the benefits of quarantine.

Setting up a quarantine tank

A quarantine tank is just like any other tank for keeping organisms. Ideally, it should stripped right down to allow for treatment where necessary. All that is required is the tank, a heater, an active biological filter, some hiding places and a light.

Figure 1: My quarantine tank.

The tank

The tank for quarantine needs to be large enough to hold the fish that will be acquired but not too large as to make medication difficult or expensive. It would be unwise to use a tank smaller than 10 gallons/37 litres, unless the fish to be quarantined are very small. Even a 10 gallon/37 L tank will be too small for some fish. At tank larger than 40 gallons/150 litres, will generally be too large for quarantine as medications will be quite costly and may be difficult to get in sufficient quantities. A tank in the range 20 to 40 gallons (75 to 150 L) is a perfect size.

A glass tank doesn't have to be used and even plastic tubs would be suitable. The main drawback with tubs, however, is it is not as easy to observe the fish. Observing the fish is important, as this is how you determine if they are healthy or not.


It is important to have an active biological filter as fish will be in the quarantine tank for some time. Without an established biological filter, ammonia could be a problem and can even kill the fish. A biological filter in quarantine tank is essentially the same as in any other tank except that the media used must be compatible with any medications that may be required. Live rock, sand and any other calcium carbonate material should be avoided because it absorbs copper. Most synthetic filter media are suitable for biological filtration and the most important aspect is surface area. The surfaces of the media provide sites for bacteria to populate and the greater the surface area, the more bacteria that can be accommodated.

Hang-on-Back type powerfilters work well when filled with media such as sponges or even bioballs. Many aquarium stores sell simple air driven sponge filters which are also satisfactory. Another option is this filter: Simple Biological Filter.

In addition to providing suitable media for the bacteria to colonise, it is necessary to establish the bacteria on the media. This is often referred to as "cycling", although the term is a little misleading because it is only after the filter is established that a cycle is present. Unfortunately, this process can take some time and until the filter is established there will be a danger of high ammonia in the tank. The process can be someone accelerated by the use of existing media from an established tank, for example, the transfer of bioballs from the display tank. Transferring water from the display tank does not shorten the process to any great extent because the required bacteria are not generally in the water column.

It is necessary to feed the bacteria to encourage them to reproduce. The easiest way to do this is to add fish food to the tank on a daily basis. Only a small amount of food is required, about as much as would be fed to one or two fish. This will simulate having a fish present without having to sacrifice a fish. Monitor the ammonia during this period and if ammonia is detected, food should be added daily and the ammonia monitored until the ammonia level drops to undetectable for at least 2 weeks. It is possible that there will be no ammonia detected and in this case it is wise to wait at least 3 weeks before adding any fish. This method works better than adding a cocktail shrimp as it provides a smaller amount of ammonia and doesn't spike the system.

Quarantine tanks set up in a hurry often have problems with ammonia and frequent water changes are required to reduce the ammonia levels. As ammonia is more toxic at a higher pH, it is helpful to keep the pH at around 8.0 if ammonia is present. This won't solve the problem but will lessen the impact.

Note: It is possible to set up a quarantine tank with calcium carbonate material, but copper cannot be used in such a tank. If fish become infected with Amyloodinium it will be necessary to move them to another tank for treatment.

Hiding places

Adequate and suitable hiding places are necessary to reduce the stress on the fish. Usually, the more hiding places that are provided, the less stressed the fish will be. Additionally, multiple hiding places allow the fish to swim from place to place with confidence.

As calcium carbonate should be avoided, PVC piping of various sizes makes ideal hiding places. The piping sizes should be chosen based on the sizes of the fish that will be quarantine. Larger fish need larger pipes but smaller fish can use both large and small pipes. Constructing caves and swim-throughs is recommended.

Glazed ceramic can also be used for hiding places and even (clean) coffee cups work well.

Note: It is possible to set up a quarantine tank with calcium carbonate material, but copper cannot be used in such a tank. If fish become infected with Amyloodinium it will be necessary to move them to another tank for treatment.


Lighting for a quarantine tank need not be fancy, but some light is required to closely observe the fish for spots, discoloration and other signs associated with diseases and parasites. A single fluorescent tube is suitable.


Unless the room temperature is 77°F/25°C or above, a heater will be necessary for the tank. The temperature of the quarantine tank should be the same as the display tank. For reef fish, the suitable range is 77 to 82°F/25 to 28°C.


It is important to provide circulation in the tank to ensure good gas exchange and oxygenation of the water. A powerhead that moves the water surface is ideal. An airstone is also satisfactory.

How long should you quarantine?

There is differing opinion on the minimum time for quarantine but there is no doubt that longer quarantine periods are better than shorter ones. I used to recommend and practice a minimum period of 4 weeks until I had Cryptocaryon (AKA marine "Ich") slip through so now I recommend and practice at least 6 weeks. Under normal circumstances, a 6 week quarantine period will allow for 2 to 3 cycles of Cryptocaryon, but it is possible for a single cycle to extend for 30 days. A period of 6 weeks adds a bit of buffer for detection.

Fish should only be moved to the display tank once they have shown no signs of infection, they are feeding well on prepared foods and have put back on any weight lost during the collection and transport period.

Last updated: May 8, 2004