How to Quarantine Marine Fish

by | Feb 29, 2012 | Advanced Aquarist | 2 comments

How to Quarantine Marine Fish

Quarantine tanks are simple and affordable, so you have no excuse. Pictured: 10 gallon tank, heater, thermometer, sponge filter (with air pump), cheap LED lights, Seachem Ammonia Alert, various medications, and one shy Earlei wrasse.

Marine Fish Quarantine: The Abridged Version

There’s no two ways about it: Quarantining new fish is not optional. Simply put, serious aquarist quarantine their new fish. When you bring home fish, you also bring home the responsibility of giving them the best possible care.  Fish dying of infectious diseases is unnecessary … and preventable.

Fish are exposed to a wide range of diseases along their entire chain of custody (collector, wholesale, retail): marine ich, marine velvet, flukes, intestinal worms, Brooklynella, bacteria, et al.  No matter how diligent the best wholesalers and retailers are about quarantining and treating their livestock (and this is the exception rather than the rule), chances are their fish will still carry disease.  It is extremely difficult for large, rapid-turnover operations to rid all diseases from their fish due to the sheer number of fish that pass through their systems.

And once disease enters your aquarium, it is a nightmare to cure and can cost the lives of all your fish.

If you can’t afford quarantine equipment and if you don’t have patience for this process, this hobby might not be for you.

Fortunately you can do something about it by quarantining new fish at home for 3-4 weeks.  For aquarists who are not regularly performing quarantine, I will provide a simple and affordable guide. I will go so far as to say if you can’t afford quarantine equipment and if you don’t have patience for this process, this hobby might not be for you.  I do not mean to come off overly preachy because I’ve also been guilty of not quarantining new fish.  Speaking from experience, skipping this simple procedure results in much more pain and hardship for you and your fish.

Disclaimer: This is not intended as the most comprehensive quarantine procedure.  My goal is to provide straight-forward, affordable quarantine instructions to encourage every aquarist to quarantine their new fish.  This article is a “living document.”  I welcome any suggestion or criticism in the comment section at the end of the article.

Here is the ten basic equipment you will need for your quarantine system:

  1. Quarantine tank: A cheap 10 gallon (40L) glass aquarium is sufficient for most small and medium sized fish. For larger fish (> 4″/15cm), consider a 20 or 29 gallon aquarium.
  2. Heater: Any small, reliable submersible heater will suffice.
  3. Thermometer:  A cheap mercury-in-glass thermometer will do.
  4. Filtration:  Quarantine systems do not require complicated filtrations.  In fact, you do not want to run advanced filtration that may interfere with potential treatments.  All you need is a simple sponge filter driven by a cheap air pump.  If you have a canister filter or hang-on power filter laying around, feel free to use it (without activated carbon).
  5. Refractometer:  I know many hobbyists still rely on swing-arm hydrometers to measure specific gravity.  Do yourself a favor and purchase a refractometer.  You will get far more accurate salinity measurements (required for some treatments).
  6. Test kits:  The two basic test kits you will need during the quarantine process are ammonia and copper.  I would also recommend Seachem Ammonia Alert to provide addition warning of ammonia spikes.  Ammonia poisoning is a very real threat to fish in small/new QT tanks and can kill quickly.
  7. Medications:  There are many medications available for treatment.  I would consider the following three medications “the essentials”: Prazipro, Cupramine*, and Maracyn Two. These three medications are gentle, effectively combat most diseases, and work well together.  I will explain more on their usage later in the article.
  8. Decorations (for shelter):  A variety of PVC pipes/fittings is all you need.  Since you will treat your tank with medication, do not use live rock.
  9. Light:  No need for anything fancy.  Even a desk lamp (preferably on a timer) will work as long as it does not overheat the water.
  10. Salt mix and good (e.g. RO/DI) freshwater.  Premix 5 to 10 gallons to have on hand for emergency water changes.

*I have since replaced Cupramine with chloroquine phosphate, which I find is easier to administer for single dose treatment of external parasites.  Chloroquine is harder to acquire than Cupramine though, so if you can not find Chloroquine, Cupramine is still a viable substitute.

And here are the ten steps to receiving and quarantining new fish:

  1. Place your sponge filter in your main tank or sump so that it cultivates nitrifying bacteria for a minimum of 2 weeks (the longer the better).  There is no need to run the air pump during this “seeding” time.
  2. When you’re ready to purchase a new fish, first prepare your QT tank. Fill the QT tank with saltwater to match the salinity of your display tank.  This water can be partially or fully comprised of water from your main tank.  Move the sponge filter from your display tank to your QT tank.  Run the air pump at this time.  Install the heater and thermometer; Match the temperature to your main tank.  Add the decorations.
  3. Drip-acclimate your new fish with water from your QT tank.
  4. Add your new fish to your QT tank.  Let your fish rest for a day.  You can attempt very light feeding several hours after introduction.
  5. On day two, medicate with Prazipro.  Follow the manufacturer’s directions.  Prazipro is pre-solubilized praziquental, a proven gentle medication that will cure fish of flukes and worms.
  6. On day seven, perform a 50% water change with new saltwater only.  Make sure the new water is the same salinity and temperature as your QT tank. 
  7. Begin your Cupramine medication after the water change. Cupramine is the gentlest copper-based medication on the market and will cure fish of ich, marine velvet, external parasites, and a number of other diseases.  Again, follow the manufacturer’s directions.  This is particularly important for Cupramine because overdosing copper is deadly to fish.  Test for copper levels to make sure you have dosed the right amount.
  8. You can also re-dose Prazipro at this time.  A single dose of praziquental may not kill some fluke species or flukes incubating in eggs.  This is one of the few times you can safely break the manufacturer’s directions (another will be cited next).  Seachem discourages the use of other medications when administering Cupramine because they do not want to be liable for any adverse interactions with all the medications available.  However praziquental has been proven safe to use in conjunction with Cupramine (and chloroquine**).  Some aquarists rely on Cupramine to take care of stubborn “leftover” flukes, but I recommend a second dose of Prazipro since praziquental is safe to use with Cupramine.  ** Note: While praziquental is safe with choloroquine, choloroquine has been shown to reduce the bio-availability of praziquental, so a second dose of praziquental during choloroquine treatment may prove ineffective.
  9. Observe your fish over the next two weeks while the two medications are doing their job.  If you see any signs of bacterial infection such as fin rot or cloudy eyes, administer Maracyn Two.  Maracyn Two is a broad spectrum antibiotic that is safe to use with the other medications.
  10. 21 days after you first introduced your new fish to the QT tank, if the fish appears healthy and feeding, congratulations!  Your fish is now ready for its new home in your display tank.  Net your fish into a specimen container.  Drip-acclimate from your display tank to the specimen container, then add your new fish to your display tank.  Do not add water from your QT tank to your display tank.

Important additional notes: During the entire quarantine process, make sure you are testing for ammonia and measuring specific gravity daily.  Top off the water as needed and perform water changes if ammonia levels begin to rise to dangerous levels.  Never add neutralizers like Amquel or Seachem Prime to detoxify ammonia because they can greatly increase the toxicity of Cupramine.  You will have to administer more Cupramine whenever you perform water changes; Add Cupramine in gradual increments and test copper levels so you don’t overdose.


This article is intended as a basic quarantine guide.  There are many methods to deal with diseases, and some fish require more special consideration than what I’ve outlined here.  For example, clownfish are prone to Brooklynella which can be treated with Formalin baths.  These alternative methods and species-specific treatments are beyond the scope of this article.  But if all aquarists adopt simple quarantine procedures such as the one I described, captive fish will live longer and thrive in the home aquaria.  For anyone who’s never quarantined before, you will be stunned by how much healthier your fish look and behave without worms, flukes, and ich.

  • Leonard Ho

    I'm a passionate aquarist of over 30 years, a coral reef lover, and the blog editor for Advanced Aquarist. While aquarium gadgets interest me, it's really livestock (especially fish), artistry of aquariums, and "method behind the madness" processes that captivate my attention.


  1. Ken

    Hi Leonard,

    I really enjoyed the article about Marine Fish Quarantine, and indeed learnt a lot of things.

    Just a quick question, I am currently using Redsea Coralpro salt, after mixing the salt with RODI water i used SERA NH3/4 test kit and realize it contains a light level of ammonia, is that normal? I also checked the RODI water is clean with the same test kit.

    From the article you mentioned we shouldnt use Prime as a detoxifier, if that’s the case how i should remove ammonia from the newly mixed salt water before introducing to the QT (as you know there is no biometric filtration from QT) , should i change another brand of salt mix?

  2. Bob Caliri

    Leonard, thank you for sharing your knowledge with the masses first and foremost. I am currently in the planning stages of starting up a display tank that will include invertebrates, fish and corals. I plan on constructing my build with the best protocols available to ensure the microenvironment is one in which all the aforementioned can thrive. With that said, I have read in many forums and watched many videos pertaining to the initial cycling of a tank and most threads suggest introducing a damsel as the first fish after completing a fishless cycle. My question is should the first fish be quarantined prior to introduction to the display tank? I am thinking that it would be wise to so as to avoid contaminating the display tank with various stages of pests and the display tank already will have substrate and rock which would complicate treatment. Am I thinking correctly or making this more complicated than it has to be? Thanks for your insight in advance.


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