Quarantining is the process of isolating new fish from your existing collection of aquarium fish long enough to ensure they are in good health.
Why quarantine new aquarium fish?
It is essential to quarantine new aquarium fish because they can carry parasites, most commonly external parasites such as ich and velvet. While there are a variety of medications that can treat these parasites in aquarium fish, the most effective ones are based on copper salts that are toxic to invertebrates, live rock and macroalgae. Many types of fish are also sensitive to copper, notably sharks, rays, mormyrids, loaches, pufferfish and many types of catfish.
Treating aquarium fish for external parasites is a major chore. The aquarium fish need to be removed from the reef aquarium or fish-only with live rock (FOWLR) community aquarium and treated in a hospital aquarium sufficiently large for all those aquarium fish to coexist safely. The display aquarium will have to be left fallow for at least a month for the parasitic infection to die out naturally. Quarantining new fish in a quarantine aquarium can prevent this unwanted chore.
Catching and removing aquarium fish can be very stressful for them. Also, moving the aquatic plants and corals about so you can catch the aquarium fish can damage them. If you quarantine new fish, it simplifies the process by letting you ensure that the new fish are healthy before they are put in the display aquarium. If necessary, you can quarantine new fish and treat them without putting any of your other fish at risk.
The quarantine aquarium
When you quarantine new aquarium fish, the quarantine aquarium doesn’t need to be particularly large or complex. In most cases, a 10- to 20-gallon quarantine aquarium will be sufficient to quarantine new fish. A tank heater is required for your quarantine aquarium if you quarantine tropical fish; otherwise, the only essential piece is a filter.
When you quarantine new aquarium fish, there’s no need for lights, and in fact, a dimly lit quarantine aquarium will encourage new aquarium fish to settle down.
Rocks, gravel, and sand should be left out of the aquarium that you will use to quarantine new aquarium fish. Calcareous minerals can absorb copper salts and then release them later on, making it difficult to precisely dose copper-based medications. Because marine fish especially are sensitive to overdosing, this is one complication you don’t want to deal with when you quarantine new fish.
The only decorative items in your quarantine aquarium should be ones made from plastic. Plastic plants can be used to provide shade and hiding places when you quarantine new aquarium fish, while PVC tubes make good burrows for nocturnal or benthic fish, such as eels and gobies. Plastic is also easy to clean and chemically inert.
There are two ways to filter quarantine aquariums. One approach is to use zeolite to remove ammonia directly. The big problem with zeolite is that once it has become saturated with ammonia, water quality in your quarantine aquarium will decline very rapidly. It is therefore essential to replace the zeolite regularly to ensure this doesn’t happen. When you quarantine new aquarium fish, use an ammonia test kit every few days to check that you are using sufficient zeolite for the amount of aquarium fish being quarantined and make sure the zeolite in your quarantine aquarium is being replaced sufficiently often.
The alternative and probably easiest approach is to use some type of biological filter in your quarantine aquarium. Plain sponge filters provide a good balance of cost and efficacy in small quarantine aquariums, while external canister filters probably get the nod for larger quarantine aquariums holding bigger or messier aquarium fish.
In either case, the biological filter you use when you quarantine new fish will need to be mature before it is pressed into service. You can do this either by removing live filter media from an established (and disease-free) aquarium, by using a fishless nitrogen cycling method prior to introducing the aquarium fish or by adding commercially available cultures of filtration bacteria to jumpstart the system.
How long you need to quarantine new fish?
For tropical fish, a quarantine period of at least a month works well. For coldwater fish kept at room temperature, this can be extended to six weeks or more to allow for the fact that parasites develop more slowly in cold water.
Because quarantine aquariums used to quarantine new fish are small, fish food should be provided only sparingly, and uneaten fish food must be removed at once. Newly purchased aquarium fish are unlikely to eat anything for the first day or so, but the aquarist should give thought to getting new aquarium fish back into good condition as soon as possible.
For example, wild-caught loricariid catfish (particularly Farlowella, Otocinclus and Panaque) are notoriously likely to be underweight by the time the aquarist has brought them home. These fish will often starve to death when simply thrown into the community aquarium straight away, so quarantining them gives the aquarist a chance to provide them with the algae and soft vegetable fish foods they need to get back into shape.
Gobies, butterflyfish, mormyrids and spiny eels are other examples of fish that benefit from a bit of fattening up in a quarantine aquarium before they are moved into the display aquarium.
Quarantining invertebrates and live rock
Quarantining invertebrates that don’t need bright light is essentially similar to quarantining fish; but invertebrates with symbiotic algae, such as corals and anemones, will require at least some light above the quarantine aquarium. This needn’t be quite as intense as the lighting over the display aquarium, particularly if the coral or anemone also receives supplementary feeding. Good-quality fluorescent tubes with reflectors should be ample for the three to four weeks required to safely quarantine invertebrates.