Do I Need a Quarantine Tank?

Imagine this: you’ve just bought a stunning new fish that will be the centrepiece of your saltwater aquarium. You’re excited to add it to its new home—but then a thought hits you. Should you place it directly into your main tank, or set up a quarantine system first? If you’re already asking this question, you’re ahead of many aquarium owners, who often only learn about quarantine tanks after disease has spread through their entire collection.

The short answer is yes, you need a quarantine tank if you’re serious about keeping a healthy aquarium. 

What is a Quarantine Tank?

A quarantine tank is just what it sounds like: A separate system used primarily for temporarily housing new fish before they enter your main aquarium. Consider it a medical quarantine ward for your aquatic pets that allows you to safely observe them for stress or disease.

The idea is not new to aquariums. Quarantine procedures are common in zoos, veterinary hospitals, and even some human hospitals to prevent the spread of disease. In the aquarium world, that could be the difference between introducing a healthy new inhabitant to your aquatic family and unwittingly harbouring some organism that will eventually kill everything in your tank.

The Secret Dangers Lurking in Your New Fish

Even fish from reputable sources can harbor diseases, parasites, or stress-related problems that are not necessarily visible right away. Fish are often good at hiding their symptoms when stressed, which is why a perfectly healthy-looking fish in the store can later appear ill days or weeks after you take it home and let its immune system relax.

White spot, velvet disease, bacterial infections, parasites, and viruses are problematic. Some of these health issues can lie dormant for weeks, and suddenly make your fish ill, while other diseases and infections can spread through your main tank within hours of introduction. Marine fish are also susceptible to other types of health issues from aquarium pests and hitchhikers like Aiptasia anemones, which can be quite destructive in reef aquarium systems.

Aside from diseases, new fish arrive with helpful bacteria collected from their former habitat, yet that may not necessarily correspond to your existing biological filter. This can result in mini-cycles within your main tank, leading to ammonia or nitrite spikes that increase stress levels in fish and make them more prone to disease.

When to Quarantine, and When It’s Fine Not To

If you are a reef keeper with an expensive load of corals and fish, the cost of draining your entire system due to losses is much greater than maintaining a quarantine process. 

Any fish from unknown origins (online, swaps, or rescue) should at the very least go through quarantine, no matter how healthy they may seem. You just don’t know what’s been done to them or what has been done in the past.

If you’re adding fish to a tank with especially sensitive or pricy inhabitants, quarantine is also recommended. As mentioned, some fish species are more susceptible to stress and disease than others; some harbor certain pathogens while not suffering from them, but can wipe out a roomful of other species.

Any fish displaying even the briefest flicker of any stress, odd behavior, or physical abnormality whatsoever should be immediately isolated, no matter what source they may have come from. This would also account for fish showing the following signs: labored hard, clamped fins, sudden color changes, and swimming abnormally.

Establishing an Efficient Quarantine System

A well-designed quarantine tank doesn’t have to be fancy. A 20-gallon tank is suitable for most uses, but larger or multiple fish might require a larger quarantine tank. 

Your filter system should be simple yet efficient. The sponge filter, which operates on the principle of utilizing a vertical type of sponge suction to remove waste products, is particularly suitable for keeping small fish and separator fish in an aquarium breeding or quarantine aquarium. Don’t use filter material from your display tank because it can transmit pathogens to and from systems.

Do not over-decorate, but do provide hiding places to ease the fish from stress. Upside-down flowerpots, PVC pipe fittings, or just plastic caves will do the job and can be easily disinfected between uses. Avoid porous ornaments such as real rocks or driftwood, as they can hold pathogens and are challenging to sanitize.

Lights should be dimmed to minimize stress, and a heater is required for temperature consistency. We suggest an adjustable heater, as this enables you to increase or decrease the temperature when needed. For optimal temperature control, the HYDROS temperature sensor helps monitor the water temperature so you can maintain it within the safe zone for your fish. 

How to Quarantine Fish Properly

New fish should be quarantined for 2 to 4 weeks. During this time, you will be monitoring the fish for signs of disease every day, while looking out for water chemistry changes and applying treatments if necessary.

Early days are the key (the time in which stress symptoms usually present). Look out for a decrease in appetite, reduced activity level, the rate of breathing, and physical appearance. When the fish is first introduced into your tank, take pictures. It’s remarkable how quickly you can lose sight of what “normal” looks like with a new fish that you look at every day

Water changes also now become even more critical in smaller QT systems, as these smaller quantities can see dramatic shifts in their water chemistry. For smaller QT tanks, you should be performing a 10-15% water change every other day, and for larger QT tanks, we recommend 25-50%. If you are treating your QT tank, you should perform a 100% water change every 3 to 4 days to remove any excess treatment solutions from the water. 

Conclusion

So, do you really need a quarantine tank? If your goal is to maintain a thriving, healthy saltwater aquarium, the answer is a resounding yes. Quarantining new arrivals is less about being overly cautious and more about protecting the time, effort, and money you’ve already invested in your display tank. It gives you peace of mind, ensures your fish have the best chance to settle in stress-free, and prevents invisible threats from wreaking havoc on your aquatic ecosystem.

Think of a quarantine tank as an insurance policy, one that costs very little compared to the potential loss of an entire aquarium. By taking this proactive step, you’re not just safeguarding your livestock; you’re also creating a more stable, balanced environment where your fish and corals can truly flourish.

And remember, you don’t have to do it alone. If you’d like guidance on setting up or managing a quarantine system, the Reefco Aquariums team is always here to help!