Fish Quarantine, the long way

There are almost as many different quarantine processes as there are aquarists in the hobby for more than 10 years. About the only thing there are more of are uninformed hobbyists who claim a quarantine is bad for fish, or who don’t want to spend the time, or inaccurately claim not all fish can or should be quarantined, or who don’t want to spend the $40. for a quarantine kit, or who don’t believe it is necessary, or who believe that a healthy fish can survive any disease or parasite. We, the Old Guard, for the most part know better. I wrote . . .more than 10 years because if you’ve been in the hobby that long, you’ve come to realize that performing a quarantine process is essential to good marine husbandry. The smarter aquarists know this from the outset and began using a quarantine process from the first day in the hobby!

What good is a quarantine process?

Benefits include:

1) Further acclimate the fish to captive life without being bothered by other fishes

2) Get the fish to eat without it ‘running away’ and hiding

3) Get the fish on the right foods and nutrients

4) Allow the fish to eat without competition

5) Give the fish a chance to recognize and become acclimated to the aquarist

6) Give the fish a chance to heal any capture or travel injury or trauma

7) Give the fish a chance to recover from any condition or disease

8) Prepare the fish for a more competitive life in the community/reef tank

9) Protect the health of the display tank livestock.

Maybe you can think of more advantages/benefits of a quarantine process? I think the best phrase I have ever seen another person post was, “Quarantine provides a new fish sanctuary.” It may sound corny but ultimately — The only thing you want to add to the marine system is the fish (as opposed to parasites, pathogens, and disease). Most aquarists as I do, have an emotional investment with the fishes in the display tank. There is a money investment too. A new fish bringing disease into the display that kills other fish can be a significant loss of monies. But for me the far greater loss is the loss of fish life for failing to protect the display fishes from new arrivals bringing in disease. Ultimately, the quarantine process is a stress reducer not an added stress to a new fish. Even though only about 1/3 novices and less experienced hobbyists perform a quarantine process, it is a process performed by all marine livestock professionals (e.g., public and private aquarium management). I can only slightly alter the quarantine process found in this excellent and comprehensive article: An Ounce of Prevention is Worth a Pound of Cure: A Quarantine Tank for Everything by Steven Pro – I disagree with the above article on one point: Length of time to hold a fish in quarantine. Four weeks is too short of time. I recommend to quarantine no less than 6 weeks. Professionals may quarantine fishes 3 or 4 weeks, but they take scrapings and/or clippings of the fish and perform microscopic examinations to identify the presence or absence of parasites and disease. Since I don’t expect the usual marine aquarist to do this, 6 weeks in quarantine is the minimum I recommend. This post is to outline my quarantine process in the context of the acquisition of a new fish; and to further detail some aspects of my quarantine process. Use it all or as much as you want, if you like what I do. Keep in mind that I can’t/won’t recommend anything less than this. Let’s jump into the water. . . NOTE: Only quarantine one fish at a time.

What you will need

  1. Equipment and Supplies (The basic setup is often available as a ‘special’ package)
  2. Properly sized bare-bottomed tank (about 5-7 gallons for every inch of fish, longer and shallow for fish like tangs that travel distances); this is the quarantine tank (QT)
  3. Lighting (enough for the fish to see their food, at least)
  4. Heater Simple Sponge Filter (corner filter) — one per 15-20 gallons of water; with air pump and air tubing
  5. Cleaned PVC piping or plastic decorations so fish can hide A place to put this QT All the usual test kits (at least ammonia, nitrite, and pH (or pH meter – see 8.), optional: alkalinity)
  6. Measuring devices: BUY the refractometer (forget using a hydrometer for hyposalinity treatments, which you’re likely going to have to do sometime if you stay in this hobby more than a couple of years), thermometer, pH meter (if you can afford $60-80 for a handheld field meter), etc.
  7. RO/DI or distilled water and your favorite artificial salt mix.
  8. Treatment equipment and medications according to: Stocking the Marine Fish Medicine Cabinet
  9. (Optional) A substrate of clean and pure silica sand is okay. Some silica sands are contaminated with carbonates and they must not be used. [Note what’s not on this list: carbonate substrate, powerheads, circulating pumps, skimmer, UV, ozone unit, landscaping, and carbonate containing rocks (live or otherwise)]


  1. The sponge filter should be in the display system (e.g., sump) and running all the time to be seeded with nitrifying bacteria to be the biological filter for the QT. It takes about 4 to 8 weeks for the sponge to be ready to serve as the QT biological filter.

Starting the QT

  1. Fill QT with water from the display tank or make up fresh saltwater.
  2. Start bio-filter (add sponge from display tank to QT and run it).
  3. Tests: ammonia, nitrite, pH, specific gravity, and temperature of the QT water.
  4. Make adjustments as needed.
  5. The QT is ready for use.
  6. Prepare and keep on hand saltwater made from artificial salts — all future water changes will use this water not display tank water. [NOTE: if the QT will not be used within a couple of days, the aquarist should keep the biological filter going by adding food to the QT and not removing it (see After Use below).
  7. Just before fish is added, siphon off any leftover foods and detritus. Just before adding fish, perform again the above (and 1. below) series of water quality tests.]

In Use Procedures

  1. Monitor and test for ammonia, nitrite, pH, specific gravity and temperature daily.
  2. Hold water quality constant and good. (IF the biological/sponge filter was not seeded or it stops working during a treatment, control ammonia and nitrites by large water changes OR use chemical absorbents (e.g., Algone) so long as the chemicals won’t and don’t interfere with any medication. Make water changes whenever any ammonia is detected; make water changes when 0.05 ppm or more nitrite is detected when quarantine is performed on fish.)
  3. Make adjustments to water daily to hold water test results in their proper range and to keep them steady (Make adjustments more often (2-3 times per day) if the biological filter is not or stops functioning.)
  4. Remove uneaten foods 1 hour after each feeding time.
  5. Make 50% or larger water changes every week or more frequently — assuming no treatment is being administered. Follow good water change techniques: how do I do a water change? (If a treatment is administered, change water according to medication instructions. If water changes are needed during treatment and the treatment isn’t over, medication must be added back to the QT water to keep medication at a constant, recommended concentration.)

After Use

The QT can remain running, with food (0.5 gram frozen food per 20 gallons) added every other day to keep the biological filter running, OR Return sponge filter to display tank system (e.g., sump) and keep it running until needed again.

Breakdown the QT

Wash and rinse it out thoroughly; let dry; store so that it can’t/won’t be contaminated or gather dust.

Things NOT To Do/Use

  1. Don’t use live rock in a QT. It may seem like a ‘short cut’ for a biological filter, but you won’t be able to treat the fish with medications — it will turn the live rock into base rock. (See What is Live Rock, Anyway? )
  2. Don’t use any carbon or general absorbing media — it will interfere with any medication you might want to administer.
  3. Avoid the use of any ‘high-end’ filtration system. Stick with a simple sponge filter. The benefits include: easy to move it into and from the display system for keeping it alive; it has no intake to injure a fish; it gently moves the water’s surface; and doesn’t create too much of a current. Your best control over water quality will be testing and making water changes. HOWEVER, if you do have to use a medication in the QT, then you might need carbon to remove the medication.
  4. Don’t count upon any of those products that say they will start your tank’s biological filter by adding bacteria. They usually won’t help you and since you may be using medication, they definitely won’t be able to help. When you use medication, many of the bacteria will die or just fail to come out of their dormant state.
  5. Don’t attempt to quarantine multiple fishes. If you would like a pair of anemone-fishes, for instance, either use two quarantine tanks or quarantine them one at a time. There’s no rush and there’s absolutely no need to put them into your display at the same time. 5.b One problem with putting multiple fishes through the same quarantine is that one fish can have a disease and give it to the rest. Now you’re treating fish that weren’t ill to begin with. Or. . .The nightmare: Every fish in the QT can have a different disease or condition and they require different treatments. It’s not worth the trouble, risk, or likely loss. 5.c Another problem is that putting multiple fishes through quarantine defeats many of the above listed benefits of using a quarantine process. Check out that list. Which of the listed benefits of using a quarantine process would be lost if multiple fishes were in the QT?
  6. Don’t assume everything is fine. Keep checking the water quality and especially pH. A water change can mend a world of hurts!

How the quarantine process fits into the acquisition of a new fish

  1. Aquarist has fish (in a bag in a box; or a bag in a bag).
  2. Acclimate the fish to its new water according to: It Was Acclimation, I know. . .
  3. Give the fish a freshwater dip according to: Freshwater Dip for Marine Fishes
  4. Place fish into QT & follow above general QT procedure.
  5. De-worm all eating fishes in quarantine. (See below reference).
  6. Treat certain fishes for anticipated diseases. See the ‘Post Acclimation’ recommendations of this reference: It Was Acclimation, I know. . .
  7. Closely monitor fish for signs of injury, illness, parasites, infections, etc. Perform any needed treatment.
  8. Get the fish starting to eat: Food Presentation
  9. Feed proper foods with vitamins and supplements according to: Feeding Marine Fish and Fish Nutrition
  10. If fish does not require treatment, continue to monitor the fish in the QT for 6 weeks. If fish was treated, then hold fish in QT for 4-6 weeks AFTER the cure is finished and the medication (if any) was removed from the QT water.
  11. After the QT time, the fish is bagged and acclimated to the display tank water according to: It Was Acclimation, I know. . . (NOTE: this could be a shorted/abbreviated acclimation IF the QT water is very close in quality and chemistry as the display tank water).
  12. ENJOY YOUR HEALTHY FISH IN ITS NEW HOME! I have done the above (or a version of the above) for more than 35 years now. For over 35 years my display tanks have been free of parasites, disease microbes, flukes, intestinal worms, etc., etc. Together with reduced stress:Stress (and the Single Marine Fish) the fish live a long and healthy life (oldest one is now 19 years old).

Take it a few steps further …

Imagine this. You just bought a brand new fish. It looks ok and it acts normal. So you decide to give it the textbook quarantine—a separate tank for about 40 days. When all looks normal, it gets added in with the rest of your stock. A short time later, you notice a problem in your tanks. The fish look sick and many are dying. What happened? You made one of the most costly mistakes a fish-keeper can possibly make—insufficient quarantine procedures. Let’s look at the mistakes more closely and then discuss how to do it right. The first and most common mistake made when people quarantine is to assume that a fish in a separate tank is truly segregated from the rest of their stock. Remember, any link between the quarantine tank and your other fish is a means of spreading disease—even you. When you put your hands in one tank and then another, you are serving as a vehicle for any diseases in one tank to spread to another. Many people believe that washing their hands and arms with soap and water in between tanks will solve the problem. Not so. Short of soaking your hands and arms in bleach, you won’t kill everything on your skin. So what can you do? The best plan of action is to take care of all business with your original stock first each day before going anywhere near the quarantine tank. After coming in contact with the quarantine tank, avoid contact with your other tanks for as long as possible—the longer the better, as fewer organisms will be able to survive the acidic, enzyme-packed environment that is your skin. And since you are going to such great lengths to make sure you transfer nothing on your skin, it goes without saying that you should never share equipment such as nets or buckets between your stock and quarantine. Once you have two separate tanks set up, two sets of equipment, and a fool-proof system for avoiding consecutive contact—you’re all set, right?  …Right?  Here is where most people make the second mistake.  They place the quarantine tank in close proximity to their other tanks—either in the same room, or even worse, right next to each other.  One half teaspoon of water from an aquarium contains between 1 million and 1 BILLION bacterial cells.  The next time you watch that bubble from your filter rise to the surface of the water and burst into millions of micro-droplets, know that each of those airborne micro-droplets can contain thousands of bacterial cells intent on infecting everything they can reach in no time at all.  Distance is very important.  Place your quarantine tank as far away from your other fish as possible. At minimum, a different room is a must.   The dictionary defines “quarantine” as a 40 day period.  Most people assume that if they have been faithful to the guidelines above, and after 40 days the new fish still look healthy, they are perfectly safe to introduce to their stock.  Here’s the hidden problem with doing that.  Many fish may look and behave perfectly normal, and yet carry all sorts of diseases.  They may carry a virus to which they are immune, a bacterium which to them is normal flora or benign—but to your other fish is a virulent pathogen, or any of a variety of sub-clinical problems.  But how will you know?  The best thing to do is to take a fish from your stock and add it to the quarantine tank.  Observe it.  Does it show any signs of illness?  Is it still eating and acting normal?  If so, great—but, you’re still not done.  The final step is to take another fish from your stock and stress it.  Leave it in a bucket for a day or two—creating an immuno-compromised state.  Add this fish to the quarantine tank.  If, after a period of careful observation, it looks healthy—chances are it will be safe to introduce the new fish to your stock.  Should the above scenario result in either of your two stock fish becoming ill, or showing any other signs of poor health, the new fish should be considered unsafe and removed from your hatchery or home.  Make sure to bleach everything which was exposed to water from that tank.