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How To Quarantine Saltwater Fish? 11-Step Guide

How To Quarantine Saltwater Fish? 11-Step Guide

Most people learned the word ‘quarantine’ only in 2020 after the unfortunate COVID-19 pandemic came around and turned our lives upside down. But, us, fish peeps, have known and used this word for quite a while now, haven’t we? 

I don’t think I need to stress how important it is to quarantine saltwater fish – or any other fish for that matter. 

In this blog, I’ll tell you all that you need to know about how to quarantine saltwater fish successfully and share a few other nuggets of wisdom along the way. 

So, let’s begin! 

10 Things You Need To Quarantine Saltwater Fish 

  • Quarantine tank
  • Filter
  • Heater
  • Thermometer
  • Refractometer
  • Test Kits
  • Medications
  • Decors
  • Light
  • Salt Mix & Water

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Quarantine Tank 

A 10 or 20-gallon tank would be enough for one fish. However, if you’re going to quarantine multiple fish, you can use a 29-gallon tank. 


A simple sponge filter (without activated carbon) should do. You don’t want to use complex filtration systems for quarantine tanks. 

As a matter of fact, if you install an advanced filtration system, it will interfere with the treatment. 


Any small, submersible heater will do as long as it is functioning well and there are no chances of you or your fish being electrocuted. 


Any cheap, mercury-in-glass thermometer will do. Once again, just make sure it is functional. 


I suggest using a refractometer instead of the swing-arm hydrometers that many hobbyists use. A refractometer offers far more accurate salinity measurements (needed for most treatments). 

Test Kits 

You will need test kits to determine the tank’s pH, ammonia, nitrite, nitrate, and copper levels. A purchase I’d recommend would be Seachem’s Ammonia Alert since ammonia poisoning is a very real and probable threat in small tanks. 


There are so many overwhelming choices to select from regarding medication. But I would recommend getting Prazipro, Cupramine, and Maracyn Two.

All three of these medications are gentle yet potent enough to combat most aquarium diseases. 

Decorations For Shelter 

You might want to add a couple of PVC pipes/fittings to work as a makeshift shelter for your quarantined fish. 

Make sure you don’t use live rocks, substrate, and filter media since these objects will absorb the treatment, making it ineffective. 


You don’t need anything fancy here. A single bulb fluorescent light hood for dim lighting would be fine. A desk lamp (preferably on a timer) works well, too, as long as it doesn’t overheat the water. 

Salt Mix And Water

Make sure you have premixed 5 to 10 gallons on hand to perform emergency water changes. 

11 Steps To Quarantine Saltwater Fish 

  •  Put the sponge filter in your main tank or sump and give it around two weeks to cultivate nitrifying bacteria. That being said, the longer the duration, the better. You don’t need to run the air pump while ‘seeding.’

  • Once you have decided to buy a new fish, you will need to set up a quarantine tank. Fill the tank with saltwater to match the salinity level of the main tank. You can partially or fully use the water from the main tank. 

  • Relocate the sponge filter from the main tank to your quarantine tank. Run the air pump. Install the heater, a thermometer, and the PVC pipes. 

  • Drip acclimate your new fish using water from the quarantine tank. 

  • Place your new fish in the quarantine tank and let it rest for an entire day. You can try very light feeding a few hours after introduction. 

  • On the second day of the quarantine, medicate the tank using Prazipro. It is pre-solubilized praziquantel, a proven medication to eliminate flukes and worms. Make sure you adhere to the manufacturer’s instructions strictly. 

  • On the seventh day, carry out a 50% water change with new saltwater. Goes without saying, but make sure the new water has the same salinity and temperature as your quarantine tank. 

  • On the seventh or eighth day, dose the water using Cupramine. Cupramine is the most gentle medication available to treat ich, external parasites, marine velvet, and a host of other diseases. Once again, stick to the manufacturer’s guidelines when dosing the medication. Carry out a test to ensure the copper levels are within safety limits. 

  • You can redose the tank again with Prazipro since once may not be enough to kill certain fluke species, particularly their eggs. This is one of those rare occasions where you can safely break the manufacturer’s guidelines. While Seachem discourages mixing its medication (Cupramine) with other medicines, so it’s not liable for any adverse reactions incurred, the use of Prazipro and Cupramine together has proven to be safely effective. 

  • Closely monitor the fish for two weeks as the medications do their magic. If, by any chance, bacterial complications like cloudy eyes and fin rot occur, use Maracyn Two. It is a broad-spectrum antibiotic deemed safe to use with other medications. 

  • 21 days after introducing the new fish to the quarantine tank, if it appears healthy, active, and has an appetite, congratulations! Your fish is ready to shift to its new home. You will have to gently net the fish into a specimen container. Be patient and drip-acclimate from the main tank to the specimen container. Next, add your new fish to the main tank. And don’t use any water or equipment from the quarantine tank in your main tank. 


During the entire length of the quarantine process, you have to make a point to test for ammonia and measure specific gravity every single day. Then, top off the water as required and carry out water changes. 

Top of the water every alternate day and perform water changes if ammonia levels rise to toxic levels. 

You should never add neutralizers like Seachem Prime and Amquel to detoxify ammonia since they react with Cupramine and create a highly toxic environment. 

Now that you are genned up on everything you need to know about effectively quarantining saltwater fish, let’s look at some advantages of doing so. 

You will need to dose Cupramine every time you perform water changes. But dose gradually so you don’t overdose the tank. 

Why Should You Quarantine Saltwater Fish?

When you bring new fish home, you also bring their ‘micro ecology’ of specific bacterial elements and microscopic fauna. Therefore, you never know what disease-mongering parasites they will leach into your new tank. Thus, it’s crucial to quarantine new saltwater fish for the sake of the new fish and the other fish’s safety. 

As you are already aware, an overwhelming majority of saltwater fish available in the trade are caught in the wild. Every year, millions of fish are sourced from oceans and seas and shipped to wholesalers in the US, who then send them to local fish stores and online sellers across the country. 

So, by the time the fish arrives at your home, it is most likely exposed to a myriad of environments (some good and some bad) and is acutely stressed from multiple transports, medications, and mishandlings.

Unfortunately, I know one too many hobbyists who will question the need to quarantine the fish as long as the ‘fish is eating well’ or ‘fish has no visible blemishes.’

Below, I’ll list a few reasons you should quarantine your marine fish. 

  • If the fish comes down with illnesses like marine ich or marine velvet, it is a lot easier to control the effectiveness of medications in a quarantine tank than it is to treat in the main tank. 

  • Most medications used for quarantine are harmful to inverts, corals, and rocks. Dosing medication in the main tank would effectively kill these organisms. 

  • Certain medications used during quarantine can wreak havoc on the tank’s biological filter or even destroy it altogether. So naturally, treating your fish in a quarantine tank will impart no harm to your main tank’s biological filter base. 

  • New fish are under stress of being packaged and shipped, giving rise to underlying diseases. Placing new fish in the quarantine tank gives them time to recover from stress and bolster their weakened immunity. 

  • It’s already hard enough for a new fish to adjust to its new home. On top of that, your older fish will most likely pick on the new kid. By placing it in the quarantine tank, you’re buying it some time to regain strength and better defend itself when placed in the main tank. 

  • Keeping the new fish in the quarantine tank allows you to observe its eating habits and temperament keenly. This will make things much clearer and enable you to make the right changes when transforming the fish in the main tank. 

Frequently Asked Questions 

How Long To Quarantine Saltwater Fish? 

The standard practice is to quarantine saltwater fish for 21 days. But the duration is subject to change depending on the fish’s condition. 

How To Quarantine Fish Without A Tank? 

I wouldn’t recommend quarantining fish without a tank. Some hobbyists reported using plastic containers instead of glass tanks. But I would like to err on the side of caution since I don’t know how these medications will react against plastic. 

How Long To Quarantine Saltwater Fish With Ich? 

You should still quarantine saltwater fish for the next 14 to 28 days after the last sign of ich is seen. This is because marine ich has a very complex lifecycle, making it hard to eradicate it completely – hence the longer quarantine requirements. 

How Long To Quarantine Fish In Copper?

You need to quarantine fish in water dosed with copper-based treatment for more than two weeks. 

What Fish Disease Should Be Targeted in Quarantine? 

Your fish may contract several possible diseases, but the three most common ones are marine velvet, marine ich, and flukes. Regardless of whether or not the fish shows signs, you should treat the fish as if it is infected. 

By the way, here’s an article that covers both copper-based and copper-less treatments to treat ich. 

White Spots On Clownfish! Copper-Free Treatment?

I’ll post in-depth blogs on how to treat flukes and marine velvet soon. Stay tuned! 

Should You Quarantine Invertebrates? 

Yes. As a matter of fact, it’s essential to quarantine practically anything that will go inside your main tank. Thus, it is recommended to quarantine shrimps, snails, anemones, and crabs. 

But what’s tricky here is that invertebrates don’t usually show signs of any illness until the 11th hour. So on top of that, the medications you would traditionally use while quarantining saltwater fish would kill invertebrates right off the bat. 

How To Disinfect My Quarantine Tank? 

Once you remove the fish, the tank itself and its equipment can be disinfected using a mild (2-5%) bleach solution. You have to make sure even the slightest traces of bleach are rinsed off before reusing the tank again. 

You should also use a chlorine neutralizer to effectively remove potential residual chlorine as an added precaution. Lastly, sundry the tank to kill surviving pathogens. 

And lastly, always use a separate siphon for your quarantine tank and disinfect it as well between uses. 

Final Words On How To Quarantine Saltwater Fish 

Setting up a quarantine tank is indispensable in owning and maintaining a saltwater tank. This is important to ensure the well-being of every fish and invertebrate that you add to the tank. And not to mention, all the hefty bills on the medication you will save down the road. 

That being said, there’s every chance that your quarantine tank turns into an incubation tank for deadly diseases. And that’s what we’re here to prevent. 

Know that quarantining saltwater fish is neither expensive. You just need the right information. 

This short crash course on quarantining saltwater fish the right way encompasses everything you need to know on the subject. 

So, make sure you don’t skip any information. 

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