A quarantine tank, often abbreviated as “QT,” serves as a separate and controlled environment primarily used for isolating new, sick, or potentially problematic fish and other aquatic organisms before introducing them to a main or display aquarium.

The QT can be used in many ways by the aquarist.  It serves as an aquatic tool to address the many challenges of aquarium ownership.  At one point it may be an observation tool, at another it becomes a hospital, and later it serves as a time-out for bad fish behavior.  The QT is a versatile tool in the aquarist tool bag.

from 1892 to 1954 all immigrants arriving in New York had to pass through Ellis Island.  It was here that a thorough medical check was performed in an effort to prevent the spread of contagious diseases in the United States.  People were examined in the “six-second physical” and if a health concern was identified they would go for a more thorough evaluation and if necessary to a hospital for treatment.  Once they were cleared of their malady they would be released to the greater New York area.

In like manner, the QT is the aquarists’ Ellis Island.  A potential new occupant to the aquarists’ tank is first released to the QT for observation.  Over the next few weeks the new occupant will adjust to the water, light, sound, and food of their new home.  During this time the aquarist is keeping close tabs of the behavior, appearance, and appetite of the new occupant.

If there are no observable problems, the new occupant can be released to the production main tank to begin a life interacting with new surroundings and other occupants.

It cannot be stressed enough that the QT is an essential part of introducing a new tank occupant.  The pathogens that are in the water from the aquarium store, and in the occupant itself can and will infect other tank occupants upon introduction.

The QT is the first line of defense in BioSecurity. Fortunately, operation of the QT is relatively easy.  So, having one is not much of a bother at all.

The purpose of isolation is to reduce the potential for production tank infestation by a pathogen.  All veterinarians and scientists alike will tell you that it is not possible to declare a new occupant pathogen free 100%.  What they will tell you is that it is a numbers game.

Pathogens have a life cycle where they must be in contact with a host or in a water environment conducive to reproduction.  Without either of these hospitable environments the pathogen will not be able to reproduce and the population numbers floating in the water will reduce correspondingly.

When the numbers of infectious pathogens fall they get to a point where the likelihood of exposure to a tank occupant becomes very low and infrequent.  If exposed, the tank occupant’s immune system should be able to address the pathogen, or the life cycle of the pathogen will progress and the pathogen will expire before subsequent contact with another tank occupant occurs.

This is the underlying process that the QT is designed to address.  The purpose of the QT is to provide an aquatic environment where pathogens can be observed, and if necessary dealt with either through chemical exposure or environmental changes or both.  The goal of the QT is to create an inhospitable environment for pathogens.  If successful, the pathogen count will drop, the new occupant will recover, and release to the production main tank will proceed.

To properly isolate a new arrival, there must be a functioning QT available for use.  So, before an acquisition is made at the local pet store be sure the QT is ready.

A ready QT is an aquarium that has been running for at least 2 weeks and has had a few small fish swimming about feeding a healthy bacterial load with nutrients and letting the bacteria establish and balance each other in the aquarium.

This is easier than it sounds.  If there is an operating production main aquarium, take a gallon or so of aquarium water from the production main aquarium and dump it into the QT.  Then fill the QT as appropriate for the tank size, adjust the water chemistry, add a few guppies and wait a couple of weeks while the water settles down.  Be sure the water is heated and aerated and filtered with a hang-on filter.

When adding guppies, or any other inexpensive fish, be certain to select fish that are dark in color.  These fish will act like canaries in the mine to warn of pathogens.

Darker colored fish make it easier to observe certain pathogens presented on the fins, bodies, gills, and mouth.  Using a UV light source above the water will further enhance the ability to detect pathogenic symptoms in the eye or other growths on the body.

SAFETY NOTE: EXPOSURE TO UV LIGHT SHOULD BE SHORT IN DURATION AND PERFORMED NO MORE THAT ONCE PER DAY. FOLLOW MANUFACTURER’S CAUTIONS.

Take the container from the pet store and submerse it in the QT water.  Let the temperature stabilize to the QT temperature for 15 minutes.  This is an attempt to lessen the shock and disorientation a new occupant will endure once moved to the QT.

Using a fish net, that is only used in the QT, fish out the new occupant and gently release it into the QT.  Do not introduce the water from the pet store to the QT.  Assume the water is full of pathogens and dump it outside or down a drain.

The new occupant will probably dart for cover which is normal.  Give it a little time before making the first observation.

For the next three weeks (21 days) the new occupant will be observed and any item of interest will be noted on an observation sheet.  The observation sheet will include the date and time of the observation and contain a summary of the water chemistry in the QT.  The observation sheet will then be used to note any behavioral or physical changes.

The aquarist should look for behaviors like those mentioned below.

Lethargy:  If the fish is less active than usual, stays at the bottom of the tank, or doesn’t respond to stimuli, it may be a sign of illness, stress, or poor water conditions.

Rapid Gill Movement: Fast-moving gills can indicate respiratory distress, possibly due to poor water quality (low oxygen or high ammonia/nitrite levels) or gill parasites.

Scratching or Rubbing:  If a fish frequently rubs against objects or the substrate, it could be experiencing skin irritation, which can be caused by external parasites, infections, or poor water quality.

Loss of Appetite:  A fish that isn’t eating or shows reduced interest in food might be stressed or sick.

Erratic Swimming:  Swimming in circles, darting around, or uncontrolled buoyancy might indicate neurological issues, swim bladder problems, or water quality issues.

Clamped Fins:  Fins held close to the body rather than spread out can be a sign of stress, disease, or poor water conditions.

Color Changes:  A pale, faded, or darkened color can indicate stress, disease, or internal issues.

Physical Abnormalities:  Look for signs like swollen body, bloated abdomen, open sores, white spots, cottony patches, or fin rot. These can indicate various diseases or infections.

Gasping at the Surface:  Fish breathing at the water’s surface might be trying to get more oxygen, suggesting a problem with the tank’s oxygen levels or potential gill damage.

Perform observation at approximately the same time each day.  If you do observe any of the above items wait until the next observation to confirm what was noted, making certain to note any further changes or developments.

In the event there are worsening observations start the diagnosis process by reviewing the common diseases here.  If more thorough analysis needs to be performed take a picture of the new arrival or behavioral video, and along with your observation sheets and a sample of water visit a vet for consultation.

As an alternative contact a Vet online and discuss the problem.

During the isolation period the aquarist should expect to perform daily or every other day water chemistry tests, noting the results on the observation sheet for the day.

Duration: The length of time an occupant should be quarantined varies, but a common recommendation is 2-4 weeks. This time frame allows for observation and ensures most diseases or parasites manifest and can be treated.

Water Quality: Regular water changes and monitoring of water parameters (like ammonia, nitrite, nitrate, pH, and temperature) are essential to maintain a healthy quarantine environment.  NOTE: if treatment is being performed through a water additive, do not perform a water exchange until directed to do so.  Follow the instructions from the manufacturer as to when to exchange water.

After the quarantine period is over and there were no observable concerns, it becomes time to relocate the new occupant to the production main aquarium.

Using a large fish net simply scoop the new occupant from the QT and gently release it to the production main aquarium.  For the next hour observe occupant behavior in regard to the new occupant.  There may be some aggressive behavior as the new occupant learns the different territories of other aquarium occupants.  This should subside as the new occupant acclimates and establishes their own areas.  Often flora becomes a place of refuge during this introduction period.

Once the introduction is complete it becomes time to address the QT and restore it to normal operation.

If there were no observable problems during the quarantine period, then a simple change of the water filter media is all that is necessary.  The QT should revert back to the normal maintenance routine and schedule.

Remember that the QT is a normal functioning aquarium with occupants and its’ own biome.  Unless there are chemical treatments associated with the quarantine period, the biome continues on as it was before the quarantine.

If there was a chemical treatment of the water it may be necessary to perform a complete water exchange.  To do this the guppies will need to be relocated to a clean container with water from the production main tank.  Empty the QT and remove all decor washing them with clean tap water and a brush.

Equipment Maintenance:  Clean and maintain equipment like filters and heaters to ensure they work efficiently.  Avoid using equipment from the quarantine tank in the main tank (and vice versa) to prevent cross-contamination.

Tank Cleaning: Clean the tank’s interior surfaces to remove algae or biofilm.  Perform a thorough cleaning  especially if there was a disease outbreak.  Use a mild bleach solution 1:10 (10%) to clean an emptied tank.  Many pathogens exist as cysts able to survive periods of no water.  A bleach solution is very effective.  Fill the tank and dilute it 10% with household bleach.  Let it sit several hours then empty and rinse, and thoroughly dry.

Hygiene:  When handling anything inside the quarantine tank, wash your hands before and after to prevent cross-contamination.  Use separate nets, siphons, and other tools exclusively for the quarantine tank.

New Tank Startup: Perform a new tank startup with the QT filling it with tap water and neutralizing any chloramine.  Add back the decor items and adjust the Ph as needed.  Other water chemistry markers will probably register at or near zero.  Adding 30% water from the production main tank will re-establish bacteria and other mineral levels.  It should be fine to release the guppies back into the QT at this point.