Marine fish quarantine: the Holy Grail… or death?
(Opinion and experience sharing article, revised and expanded. Only a veterinarian is authorized to diagnose and prescribe treatment in Canada.)
The philosophy of a “gray and not black or white” quarantine
In the aquarium world, quarantine is often presented as a silver bullet to prevent the introduction of disease into your main tank. However, in my opinion, drawn from decades of importing and handling marine fish , there is no "black and white" answer.
• “Success” side : Some very disciplined aquarists will know how to set up a rigorous quarantine and will succeed in effectively protecting their main tank.
• On the “failure” side : The majority, unfortunately, find themselves on “ death row ”, due to lack of time, knowledge or adequate equipment.
Why? Because quarantine requires discipline , equipment , space , and most importantly, patience . Many people want to fill their reef tank right away; they can't imagine spending months running an empty quarantine tank, then putting one or two fish in at a time for several weeks, while the main reef remains virtually deserted. In practice, even the best intentions evaporate in the face of impatience.
My personal experience and the question “quarantine or not?”
After years of observing practices in my store and at my customers' homes, I have found that:
• More fish are doomed by botched quarantine than by no quarantine at all.
• It is often better to invest in quality fish, from good importers who have veterinarians and preventative treatments directly on site (even if it costs a little more).
Indeed, some diseases like ick (Cryptocaryon) are often benign in a healthy reef and do not decimate the fish population. The only disease that I think is really worth tracking in quarantine is marine velvet (Amyloodinium ocellatum), also called odinium or “velvet”. This is rarer , but extremely fatal .
The strength of a good supplier
In my case, I am not looking to buy the cheapest fish in the world. For over 25 years, I have been using the same suppliers , who are able to select healthy fish, already treated or checked, and who greatly reduce the risk of velvet. It is far from infallible, but it works : in terms of quantity, we (the store) and the fish all win.
The risks of not quarantining
Even by reducing the probability of transporting a fish carrying velvet, zero risk does not exist.
• If you unfortunately introduce a fish carrying Amyloodinium into your tank, it is often a disaster : the velvet quickly decimates the other fish, with no possibility of treating it directly in the reef (because most treatments are toxic to corals and invertebrates).
• You will then need to take all the fish out to treat them separately (with the help of a veterinarian, if you are in Canada), and leave the main tank without fish for at least 8 weeks , the time it takes for the parasite to disappear in the absence of a host.
If you opt for quarantine…
So ask yourself: do you have the budget, time and resources to quarantine properly ?
• Yes : it is an excellent choice to minimize risks, provided that strict protocols are followed.
• No : take the risk of not doing so, knowing that buying quality fish from reliable suppliers remains your best chance of avoiding velvet.
Practical guide: Quarantine procedures
(The following is a detailed supplement for those who actually want to implement a strict quarantine.)
4. Procedure for introducing fish into quarantine
1. Acclimatization
• Use the drip acclimatization method or, failing that, a gradual mixing of water.
• Avoid any osmotic or thermal shock ; in general, allow 30 minutes to 1 hour to limit stress.
2. Close observation
• Monitor the fish's breathing , appetite , swimming, and responsiveness to light.
• Look for any suspicious signs : white spots, golden veil, spots, injuries, etc.
3. Plan the duration
• 4 weeks minimum . Some go up to 6 weeks, especially if there is a health concern or a history of infestation.
• Less than 2 weeks is almost useless. More than 6 weeks, beware of chronic stress.
5. Daily maintenance and prevention of “death row”
1. Regular water changes
• 10 to 20% per week (or twice a week) with seawater of the same salinity and temperature.
• Avoid the accumulation of pollutants in small volumes.
2. Parameter control
• Ammonia at 0 ppm. Any increase indicates a problem.
• Nitrites at 0 ppm.
• Nitrates below 20 ppm ideally.
3. Stress monitoring
• A healthy fish almost always eats .
• Avoid staring at him for too long (look = predator).
• Dim or turn off the lights if he seems panicked.
4. Measures against diseases
• In Canada, all treatment must be done under the supervision of a veterinarian.
• Do not use any illegal or unapproved medications.
6. Special cases: use of treatments
• Preventive treatment?
• Some aquarists administer copper , formaldehyde or other prophylactic treatment. This can stress the fish and kill biological filtration.
• Consult a veterinarian to assess the benefit/risk ratio.
• Natural remedies or essential oils
• Their effectiveness is controversial and incorrect dosage can be dangerous.
• Here again, call on competent specialists.
7. Transfer to the main bin
1. Health status validation
• The fish has been eating well, swimming normally and has been symptom free for at least 2 weeks .
2. Acclimatization
• Make sure the salinity and temperature of the main display match, then drip or mix gradually to limit stress.
3. Avoid cross contamination
• Use a separate net , hose and container for transferring.
• Clean and disinfect all your quarantine equipment (including your hands) after use.
8. Conclusion
Quarantine is not a “magical” concept or a necessary passage:
• Poorly managed , it often dooms more fish than it saves.
• If successful , it can actually protect your main tank, especially against the more devastating Marine Velvet .
So it's a matter of weighing the pros and cons based on your budget, your patience, and the trust you have in your suppliers. And remember: no protocol can replace the expertise of a veterinarian in the event of a serious illness.
My advice : always prioritize the quality of the import and the stability of the fish before purchasing, rather than relying on a haphazard quarantine.
— Stéphane (Passionate and pragmatic aquarist for over 25 years)
Basic Equipment and Maintenance for a Quarantine Tank (40 to 75 Gallons)
1. The ideal volume: between 40 and 75 gallons
For most reef aquarists, a quarantine tank of about 40 to 75 gallons is a minimum. Check out our suitable rectangular aquariums here .
-
Why not smaller?
- In a small volume (e.g. 20 gallons or less), parameters (temperature, pH, salinity, etc.) fluctuate too easily. This puts more stress on the fish.
- Some marine specimens (e.g. surgeonfish, dwarf angelfish, etc.) need sufficient space to swim, even during quarantine.
2. The aquarium and its installation
1. Bare aquarium (without permanent decoration)
- No sand or live rocks to avoid trapping waste and parasites.
- Dimensions: Ideally a rectangular tank for good water circulation and maximum observability of the fish.
2. Support/stability
A sturdy table or aquarium cabinet that can support the weight (40-75 gallons averages 150-280 liters, or over 150 kg). Check out our suitable furniture here .
3. Cover or mesh
To prevent stressed fish from jumping: Red Sea DIY Aquarium Net Cover 36" .
This net allows good ventilation while securing your aquarium.
4. A well-cycled aquarium
It must have been running for several months with a fish in it to preserve the bacterial cycle. This fish will need to be removed when the quarantined specimen is added and put back later. An ideal option for this fish is a chromis or damselfish, hardy species suited to this type of role. Check out our Chromis and Damselfish here .
3. Filtration and brewing
1. Internal or Hang-on-Back (HOB) Filter
- Type: A simple cartridge or foam filter may be sufficient, as long as there is a biological support (ceramics, porous blocks, etc.) previously cycled.
- Objective: To maintain good water quality and proper circulation, without resorting to a complex live rock system.
2. Mixing pump / bubbler
To oxygenate the water and avoid dead zones. Discover our air pumps here .
- A moderate flow rate may be sufficient (e.g. 500 to 800 L/h mixing pump for a 40 gallon).
- Some people add an air bubbler or diffuser for extra oxygen, especially if the fish is weak.
4. Heating and temperature control
1. Adjustable heating
- Suitable power: about 100-150W for 40 gallons, 200-250W for 75 gallons.
2. Thermometer
Essential for checking temperature daily. Explore our thermometers here .
Marine fish are very sensitive to temperature fluctuations; aim for a range of 79-80°F.
5. Minimal lighting
No need for powerful lighting like for a reef tank with corals. A simple LED or fluorescent tube is enough to observe the condition of the fish. Soft light: Reduces stress in newly introduced fish.
6. Removable hiding places
Use PVC pipes, terracotta pots or easy-to-clean resin decorations. These hiding places offer fish a sense of security without the risk of trapping parasites or complicating any possible treatment.
7. Testing and monitoring parameters
Recommended instruments:
- Hanna Marine Salinity Tester
- Hanna Instruments for ammonia, nitrite and nitrate testing.
Frequency: Regular testing at least twice a week, or even daily at first to make sure everything remains stable.
8. Maintenance equipment
1. Net and siphon
Dedicated only to quarantine to avoid cross contamination with the main tank. Discover our range of products for cleaning and maintenance here .
2. Reserved bucket
Use a dedicated aquarium bucket for water changes and transport to avoid chemical residue.
3. Water heater or salt mixer
9. Basic maintenance
1. Water changes
- About 10 to 20% per week (depending on organic load).
- Use fresh, well-mixed seawater to avoid osmotic shock.
4. Suitable diet
- Boyd Vita-Chem Marine 4 oz
- Prioritize quality food. Explore our frozen food collection here .
In summary
A quarantine tank between 40 and 75 gallons is a good compromise, providing stability and comfort for most marine fish. By following these tips and using the right equipment, you will increase your chances of a successful quarantine with complete peace of mind.