19 Common Quarantine Procedure Mistakes (And How to Avoid Them)

Alison Page

Alison Page


Common Quarantine Procedure Mistakes

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As an experienced tropical and coldwater fish keeper with over 40 years of experience, I can state with some authority that the best way to keep diseases and parasites out of your aquarium is by quarantining all new aquatic life before adding the newbies to your main tank.

Now, you’d think that putting your livestock in quarantine is a relatively simple process. All you need to do is set up a clean aquarium, put the fish in it for a couple of weeks, and observe them until you’re sure your new pets are disease-free, right?

Unfortunately, it’s not quite as simple as that, and you can make plenty of mistakes. So, I decided to put together this guide to help you get it right every time.

Keep reading to learn the most common fish quarantine procedure mistakes and, most importantly, how to avoid them!

Key Takeaways

  • Quarantine new fish for at least four weeks to ensure they are disease-free before introducing them to your main aquarium, as many diseases have incubation periods.
  • Maintain a clean and separate quarantine environment, using disinfected equipment and avoiding cross-contamination with the main tank to prevent the spread of disease.
  • Monitor and care for quarantined fish diligently, observing daily for signs of disease, maintaining proper filtration, ensuring adequate oxygen levels, and acclimating them correctly before transitioning to the main tank.

Common Fish Quarantine Procedure Mistakes

However, some common fish quarantine mistakes are often made by newcomers to the hobby, and these can be catastrophic, even resulting in mass fish kills.

Using Dirty Equipment

man catching fish in the fish tank

The whole point of a quarantine tank is to create a pristine, disease-free environment in which to put new fish and other aquatic creatures until you’re sure they are completely healthy. So, the last thing you want to do is use a piece of equipment that’s dirty and contaminated with bacteria.

Before you set up your quarantine tank, clean everything, including the tank, with bleach or vinegar solution to kill any bacteria hiding there and remove dust and debris that could potentially harm your fish.

Using a Short Quarantine Period

Quarantine Tank

Some diseases take a while to develop, and if your quarantine period is too short, you could inadvertently introduce serious problems into your main tank. That’s especially common if the fish you bought are wild-caught.

For that reason, I recommend a quarantine period lasting at least four weeks.

Placing the Quarantine Tank Close to Your Main Aquarium

two aquariums with fish

Don’t put your quarantine tank right next to your main display aquarium.

That presents a risk of cross-contamination, so to be safe, always keep your quarantine tank at least 10 feet away from your main display.

Not Using the Float and Release Acclimation Method

Don’t use the drop acclimation method to introduce new fish to your quarantine tank. There are two reasons for that:

  • Bag water from your local fish store will contain any bacteria or parasites present in the store display tank and will contaminate your quarantine tank.
  • Using the bag water could change the pH or specific gravity (in saltwater) in your quarantine tank, potentially stressing the fish.

Adding More Fish to an Existing Quarantine Setup

Adding Fish to a Quarantine Tank

If you already have some fish in a quarantine tank, don’t be tempted to add more. That could introduce new diseases to the environment, meaning you would have to start all over again.

Be patient; only add more fish once the current occupants have been moved to your display tank.

Failing To Observe Your Fish During Quarantine

Once the new fish are settled in the quarantine tank, you must spend at least ten minutes observing them every day. Look out for physical symptoms of a disease, such as white spots, ulcers, and swellings, and watch the fish’s behavior. Flicking and scratching against solid objects in the tank, labored breathing, lethargy, and not eating are all signs that your fish have some kind of infection.

For example, fish with Velvet disease often never show physical signs initially, but they will often swim into the flow from a powerhead or filter outlet. This disease causes fish to be sensitive to bright light, so if your fish are hiding away, that could be indicative of infection.

Putting Too Many Fish in the Quarantine Tank

goldfish in bowl

Never overstock the quarantine tank or house incompatible species together. Ideally, you should quarantine one or two fish at a time, as overcrowding causes stress, which potentially leads to disease outbreaks.

If you must quarantine territorial or aggressive fish, create compartments within the quarantine tank using dividers or plastic egg crates.

Failing To Cover the Quarantine Tank

Always cover the quarantine tank with a lid or cover slide, especially if housing notorious jumpers.

Some fish species become highly stressed during transit to their new home and are known to leap for freedom. That won’t end well if your new fish ends up on your living room carpet!

Using Rock in the Quarantine Tank

Adding Rock to a Quarantine Aquarium

Avoid using live rocks or wood in your quarantine tank, as they can absorb medications and copper, making it tricky to keep the water parameters stable.

Instead, use plastic caves or pipes to provide hiding places, ensuring no sharp or rough edges could injure your fish.

Not Using Biological Filtration

Man hand putting new aquarium bio filter medium for the filter bacteria.

Always use biological filtration in your quarantine tank, and don’t rely solely on partial water changes to control levels of ammonia, nitrites, and nitrates.

It’s all too easy to put off a water change for a day or two, but that can be fatal if you are not running an efficient filtration system.

Failing To Cycle the Quarantine Tank

As with your main aquarium, you must cycle your quarantine tank before introducing fish to it.

That’s a potential problem if you need to remove a sick fish from your main aquarium for treatment. However, a hospital tank can be small, so you can use water from your existing tank.

However, if you plan on buying new fish to add to your main display, you’ll need to set up a new tank and cycle it before bringing them home.

Failing To Test the Water

testing aquarium water

Test the quarantine tank water regularly for ammonia and nitrites, and carry out partial water changes to dilute medication build-up and remove toxins.

Providing Inadequate Gaseous Exchange

Most fish medications will remove oxygen from the water, potentially leading to oxygen deprivation, which could harm your fish.

You can combat that by directing a powerhead toward the water’s surface or using an air stone.

Adding Medications Directly to the Quarantine Tank

When you’re treating the tank water with fish medication, don’t add the drugs directly to the tank. Instead, mix all treatments in a beaker or glass cup before adding them. Use tank water to dissolve or mix the drugs, and then slowly add the diluted medicine into the filter outlet or filter chamber.

Cross-Contaminating the Quarantine Tank

Do not cross-contaminate the quarantine tank with water or substrate from your display tank and vice versa.

The idea is to get rid of the disease, not create a continuous circle of reinfection! The same goes for equipment, such as fish nets, etc. I keep a separate equipment box for my quarantine tank, and I recommend you do that, too.

Not Vacuuming the Quarantine Tank

A man vacuums a fish tank

Use a length of airline tubing to siphon uneaten food and fish waste off the tank bottom to lighten the load on your biological filter and keep the environment clean for your fish.


Feeding fish in fish tank

Newly acquired fish and those recovering from diseases typically have decreased appetites. Therefore, two small meals daily is all they need.

If you overfeed the fish, you will be left with decomposing uneaten food on the tank floor, adding to pollution levels and potentially harming your fish.

Moving the Fish to the Display Tank Too Soon

As mentioned earlier, you should allow at least four weeks before moving your fish from the quarantine tank to your main display aquarium. Don’t make the rookie error of assuming the fish are disease-free after just a week or two and transferring them.

Your new fish should appear perfectly healthy, active, and eating well before you consider moving them across to their new permanent home.

Not Acclimating New Fish Post-Quarantine

Although the water parameters and temperature in the quarantine tank should mirror those in your main display aquarium, there might be some slight variance. To avoid stressing your fish and causing temperature shock, I recommend taking the time to acclimate the fish correctly before adding them to your main tank.

In Conclusion

Although placing your fish in quarantine for at least four weeks before adding them to your main display aquarium is highly recommended, there are quite a few ways to get that wrong.

Use clean equipment when setting up and cycling your quarantine tank. Never use the same equipment for both your quarantine setup and your main tank. Carefully acclimate the fish before adding them to it, keep the tank clean and properly filtered, and don’t overfeed your new livestock. Although you’re bound to be keen to add your new fish to your main display, don’t be tempted to cut short the quarantine period, even if the fish look healthy.

Follow the simple rules provided in this guide to ensure you don’t make these common quarantine procedure mistakes!

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