Quarantine is a very common term nowadays. Fortunately, COVID-19 doesn’t touch fish but other common fish diseases do. That’s why quarantine for fish is sometimes needed.

Almost every aquarist, whether they have a reef tank with marine fish, tropical fish, freshwater fish or whatever their main tank is, sooner or later, suffers from the unpleasant problem of fish diseases. In many cases, when we first notice something is wrong and we notice one or more sick fish, administering the correct treatment is very complicated or even impossible. Therefore, it is of absolute importance we, the fish keepers, take every step in making sure our fish have the best water quality and overall environment for living in.

The pathogens of most parasitic infections or viral infections are introduced into the aquarium by means of newly purchased fish, plants, molluscs or live foods. While in the latter case, the replacement of live food with frozen food usually eliminates the threat of having external parasites, in the remaining cases we should quarantine new fish to allow observation and inspection before adding new fish to our main display aquarium. In case of occurance of external parasites on the new fish or plant, the rest of the aquarium fish will be not infected by the new inhabitant of the fish tank. Moreover it’s easier to treat external parasites in one fish instead of the whole tank.

Usually, traders and breeders ensure the complete health and quarantine of the fish sold, but a reasonable aquarist should remember that many diseases are asymptomatic at the beginning or become active when a fish’s environment changes, so even new fish from a reliable local aquarium store, before introducing them to the community aquarium, are better off in a quarantine tank for a period of time. Fish quarantine should last at least 2-3 weeks, although for some valuable species even 3 months is recommended to safeguard the fish’s health. This process is also designed to acclimatize new fish to the conditions that will be in the home aquarium, which is particularly important in the case of extremely sensitive fish. Remember that the fish’s immune system is weakened because of the transport and changing the environment so it’s more likely to be infected by other fish with bacterial infection or fungal infections. If you do’t want ot have a chain reaction in your fish tank, quarantine new fish and maintain the best water quality. This will surely help it to acclimatize in the new habitat.

Quarantine aquarium

When preparing a quarantine aquarium, consider the size and number of fish and their needs. Overstocking will result in stressed fish and poor water quality and certainly not have a positive effect on the condition of residents and instead of helping to prevent diseases – it can cause them.

A quarantine tank will work best so without substrate, decorations, or plants. In a bare bottom aquarium, it is easiest to keep order, because uneaten excess food and fish waste can be easily removed from the bottom. If hiding places are necessary – these can be added but must not affect the water parameters and should be easy to keep clean, e.g. porcelain pots. A tank without a substrate will not work for digging fish, which will not feel very comfortable in an empty aquarium. A thin layer of sterile sand or gravel will work best in this situation.

Your hygienic aquarium should be equipped with a filter appropriate to the size of the tank. The type of filter does not matter much here, it is important that it is cleaned prior to use. A heater and a thermometer are also necessary to help maintain the right temperature.

The parameters of the water in the quarantine tank should not differ from that of the target aquarium. It is best to use about 70% of the water from our aquarium, and the rest should be refilled with fresh, treated water. Regular changes and checking of parameters are important, as sudden changes can negatively affect the health of the fish, which are particularly sensitive during this period.

During the quarantine period, the same equipment and devices should not be used in both aquariums because we do not want to accidentally transfer pathogens and accidentally transfer bacterial infections and end up with more infected fish.

Observation of fish during quarantine

During quarantine, aquarium fish should be carefully monitored, paying particular attention to the following things:


It is worth observing new fish while feeding. A healthy fish should ingest food and not spit it out. Sometimes fish lose interest in food for a while after the stress caused by transport and the change to their environment. It is not a disturbing symptom yet, provided that it disappears on its own after 1-2 days in a quarantine aquarium. Sometimes a slight increase in water temperature or a varied diet makes the fussy eaters regain their appetite. Otherwise, attention should be paid to the presence of other symptoms that indicate a medical condition.


If they are long, threadlike, and trailing the fish, it is likely the fish has some internal parasites. The visible redness of the anus and bloody feces, which indicate inflammation of the gastrointestinal tract, also causes concern. In the first case, appropriate treatment should be introduced as soon as possible, and in the second, a few days’ fasting should be applied.

Fin Condition

Even if the fish’s fins look perfect after they are brought from the stores, this may change in the next few days. If the fins become jagged, drooped, stick together, or tarnish. Diagnosis and treatment should be initiated as soon as possible. It is likely your new fish is suffering from fin rot, which if left untreated can eventually cause secondary bacterial infection. That’s why every aquarist should observe his fish’s body constanly to act the fastest as possible in case of any health problem.

Skin Condition

As we do not place decorations or other elements in the hygienic aquarium that the fish could accidentally injure themselves, any changes that occur on the fish’s skin should be treated as a disease symptom. These include any damage to the fish’s body (gills, scales, ulcerations, ecchymosis, tarnish, as well as darkening and loss of color). These are all symptoms of an infected fish so they should not be underestimated and treatment should be started or infected individuals isolated as soon as possible.


Many diseases in the early stages do not show obvious symptoms, only a change in behavior indicates that something is wrong with the fish. The most common early symptoms of the disease are apathy or excessive nervousness with rubbing against objects. It is also disturbing if the fish starts to swim in an unnatural way, e.g. swinging from side to side, it often swims to the surface trying to gasp for air or falls to the bottom.

Prophylactic baths

Some aquarists, after acclimatization of fish in a quarantine tank, prophylactically use chemical baths for the most common fish diseases. The most popular agents with the broadest spectrum of activity are methylene blue and MFC. Such a procedure allows us to eliminate the risk of many fish diseases before the first symptoms even develop, but, the downside is that it can weaken the fish which will already be tired with transport, making them, paradoxically, more susceptible to disease. Therefore, it is better not to use any chemicals in individuals not showing any disturbing symptoms and to be content with careful observation if you want to keep your fish healthy. Some aquarists adivise to proceed baths with aquarium salt from time to time for prophylactics but before you decide to add aquarium salt to the fish tank, collect as much information about the species that is going to have the bath. Many species of aquarium fish are very sensitive to salt concentration so in our opinion it’s good to add half of the dose advised by the manufacturer and observe the reaction.

Snail quarantine

Not only fish should be quarantined – disease carriers are often aquarium snails. Especially those sourced from an unreliable source. Snails can be, inter alia, a source of some parasites, such as spherociliates, which die if a host (fish) is not found within a few days. Snail quarantine should last at least about a week. For this, a small aquarium or other glass vessel is enough.

Plant quarantine

Plants introduced into the aquarium can also become a source of fish disease. To eliminate the risk of disease introduction, it is best to store a new plant in any container filled with demineralized water for a minimum of one week before placing a new plant in the tank. Before that, you can (depending on the delicacy of the plant) rinse it with a disinfectant, e.g. chloramine or potassium permanganate. Plant quarantine is designed to get rid of unwanted “guests” such as hydra, fleeces, snail roe, and spores of various parasites and reduce the chances of fungal infections.

After quarantine

After few weeks of successful quarantine, and especially in a situation where we were forced to treat fish from any fish disease – both the entire tank and equipment should be disinfected and let dry for a few days before reusing. The filter should be biologically reactivated. Do not pour water from the quarantine tank into the main display aquarium, even if no disease symptoms are observed. Also, no further quarantine should be carried out in it before disinfection.

What if there are no conditions for quarantine?

Many, especially beginner aquarists, explain the lack of equipment (another fish tanks and equipment) for providing a quarantine setup. In this situation, a substitute (but always only a substitute) can be to use the fish’s current aquarium in the shop or breeders aquarium. Do not buy new fish immediately after they appear for sale, instead “visit” them from time to time, watching for changes in fish’s body appearance or behavior. If we really want to buy (we are afraid that someone will beat us to it), you can try to communicate with the seller and, for example, buy the fish and ask them to hold onto it for some time. After bringing the new fish home and before placing them in the aquarium, you can also use a short-term prophylactic bath in preparations with disinfecting properties available on the market (always in accordance with the manufacturer’s instructions). However, none of these treatments can replace a properly carried out quarantine, so if we want to avoid serious health problems of the farmed fish, the best option is to invest in an additional fish tank, which will also be useful in a situation where, despite the chemicals used, the fish needs to be treated.

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