How We Quarantine Fish

Why Quarantine?

While our main focus is coral, we do a lot to keep our fish healthy for our display. Because many of the fish we keep in our display come from importers with very crowded systems, it is extremely easy for disease to infect your fish. We therefore encourage QT for all new additions for your system.

We based our QT method on the marine collector's method of QT. It does read as rather extreme, but every aspect of it has a purpose, and, after performing this QT method personally on several fish (including some delicate specimens like cleaner wrasses), I am confident in it and endorse it.

The method of quarantine we will be presenting here is very effective in preventing brooklynella, cryptocaryon (marine ich), amyloodinium (marine velvet), uronema, internal and external flukes, intestinal worms, and several nasty bacterial issues. It is a 14 day quarantine, and is involved, but is the fastest way to clean out a fish I know of.

What do I need?

To get started, you will need some medications, a tester, as well as a proper setup.

Medication list

There are several medications used for this regimen. Here are the ones we use.

  1. Copper Power: this is for marine ich and velvet. Make sure you get the marine version (which is blue)!
  2. Seachem Metroplex: this is an anti-protozoan.
  3. Seachem Kanaplex: this is an antibiotic (gram negative).
  4. Seachem Focus: this is needed to bind medications to food.
  5. Praziquantel (powder): this is used for de-worming the fish
  6. Prazipro (liquid): this liquid form of praziquantel is used to treat external flukes
  7. Formalin: We use 37% formaldehyde with 15% methanol (this stuff is very dangerous, please use with caution)
  8. Nitrofurazone: another antibiotic. This is used to prevent secondary infections.
  9. Hydrogen peroxide (normal, 3% hydrogen peroxide).

Equipment list

  1. Bare bottom 10 or 20 gallon system.
  2. Seachem ammonia alert badge.
  3. Full bag of salt (fish only salt is fine, we recommend aqua forest's fish salt for cost).
  4. Salinity checker (we recommend refractometers).
  5. A gas mask for working with formalin (seriously. please do this in a well ventilated area).
  6. Two spare bins for temporary housing (something that can hold a couple gallons -- buckets are fine).
  7. A simple LED light for observation. Nothing expensive, just so you can see the fish.
  8. Hannah high range copper checker (HI 702). This is very important.
  9. An accurate method of measuring water. The correct water volume is very important! Take the time to measure.
  10. A sponge filter and an airstone. Aeration is crucial.
  11. Appropriately sized heater.
  12. Nitrile exam gloves (LOTS).
  13. 3 mL syringe (this is a good resolution for medications).
  14. Large diameter PVC pipe sections for shelter.
  15. A lid that covers the top of this system.

How do I do it?

Follow the following procedure, only deviating when necessary.

Important notes before we get started

Water volumes and dosage

Please note that all doses here are for your water volume not the tank volume. For example, my 20 gallon long holds about 15 gallons of saltwater. I measure out the gallons individually, and fill the tank with as close to 15 gallons as I can reasonably measure. When dosed accurately, these medications are not an issue. But when overdosed, they can stress certain species.

Copper sensitive species

Some species (mandarin dragonets / seahorses) have absolutely no copper tollerance, and cannot be quarantined with this method.

Other species (such as wrasses) will need to be slowly ramped up to the full copper level, so do this before starting the 2-week treatment. I start wrasses at 1.0 ppm and ramp up to the full treatment over the course of a couple days. For these species, just modify the starting dose, and extend the treatment to keep them at full strength copper for 14 days.

It is very important to do your research here. Some sensitive species are listed here.

Start with healthy specimens

This regimen is intense, and may not work well for very unhealthy fish. When picking out a fish, make sure they are eating and showing no physical signs of disease.

If you do elect to treat an unhealthy fish before this QT, we recommend you treat for the relevant disease before starting this protocol.

Getting ready for your new fish

  1. Set up the system at least ten feet away from your display, ideally in a different room (away from an HVAC return). Amazingly, cryptocaryons are small enough to aeresolize and travel to your display through water droplets in the air! 
  2. Mix clean saltwater to 35 ppt. Lower salinity makes copper more toxic, so it is important to retain 35 ppt water throughout treatment.Dose the water to 2.5-2.8 ppt with copper power. There is a great calculator here. After dosing, verify via the copper checker that your copper level is in the 2.5-2.8 range. We encourage you to double check this level, as it is absolutely critical. Most quarantine methods treat with copper for 28-30 days as a margin of error for incorrect copper doses. If the fish stays in this range for the full 14 days, this is not necessary.
  3. Add heaters, airstones, ammonia badge, and sponge filter. If you have access to fritz turbo start, it is a great idea to dose that as well. Otherwise, I like to dose microbacter 7 into the system and pay attention to the ammonia badge. It should stay in the green or yellow zones at all times throughout treatment.
  4. Add PVC sections to give your fish a few spots to hide.
  5. Add the lid to the top. Fish will jump. It is a real shame to lose them that way.

Acclimation procedure

  1. Mark the water level with a sticky note on the QT system.
  2. Drip acclimate the fish with the QT water. I usually do this for at least 30 minutes, but, if the salinity in the bag is really low (20 ppt, for example), drip util the water they are in is at least 33 ppt. Drip should be fast enough that temperature is retained, but not a constant stream of water.
  3. Refill the water that was removed back up to the sticky note.
  4. Once the fish has been acclimated up to 35 ppt, we will be giving it a H2O2 bath.
  5. In a separate container with freshly mixed, well-aerated, medication-free saltwater, add 1.25 mL of 3% hydrogen peroxide per cup of saltwater (20 mL per gallon). Let the fish bathe in this solution for 30 minutes. Make sure the water is well aerated throughout.
  6. Move the fish to the QT.
  7. Dose nitrofurazone (200 mg for every 10 gallons) into the QT system. This is a very mild antibiotic, so don't worry too much about overdosing. Do make an effort to get close to that target, though. Your water will become yellow. For reference, the seachem scoops will measure about 250 mg.

Nightly treatments

Yes, you read that right. We have nightly treatments in our QT system. These are mainly preventative doses to keep flukes at bay (so we don't have to treat them separately).

Nights 1, 3, 5, ..., 13

On these nights, we dose formalin into the tank. We do so at a low concentration of 1 mL per 10 gallons. It is highly encouraged to do this in a well-ventilated area, and wear a gas mask anytime you work with formalin. Formalin is a known carcinogen, so please take this seriously. Wear nitrile gloves, and use a syringe specifically for the formalin dosing.

If you are not comfortable dosing formalin, simply skip this step.

Nights 2, 4, 6, ..., 12

On even nights we dose prazipro. Follow the instructions on the bottle, and be sure to dose to the water volume. Some wrasses tend to show signs of stress when this medication is overdosed even slightly.

Formalin baths

On days 3, 6, 9 and 12 we do a formalin bath. Prep a container with freshly mixed saltwater (heat to match the QT temperature), and heavily aerate the water with an airstone.

Again wearing a gas mask and working in a well-ventilated area, add 1 mL of formalin per gallon of bath water. Add the fish to this bath, and let them bathe for 34 minutes. Maintain aeration. It is also wise to have a lid for this container, as some species will jump at the start of the treatment.

Do not do this if your fish has any open legions (visible red sores).

If you are not comfortable with working with formalin, please don't. Instead, we recommend a freshwater or hydrogen peroxide bath instead. Formalin is extremely effective against uronema and brooklynella, so, unless you are treating fish that are very prone to those diseases (e.g. clownfish and chromis), you may consider skipping this step.

We treat all of our fish with formalin, but have the luxury of a specific QT room that is used for fish quarantine only, and can be easily vented for our safety.

Water changes

While the fish is in the formalin bath, we recommend a 100% water change. Pull the sponge filter after giving it a good squeeze, remove just the sponge from the system (to save some bacteria), and replace the rest of it into the system.

Literally drain the water completely, fill it with freshwater (tap water is fine), scrub down the sides with a sponge, let it sit for 10 minutes with the airstone and sponge filter housing running (without the sponge itself).

Drain the water again, and dry the system as well as you can with a towel.

Fill the tank with new saltwater, pre-dosed with as close to the same level of copper as possible. When the fish has finished their formalin bath, simply add them back into their freshly cleaned system. Make sure to re-dose the nitrofurazone!

Dose some beneficial bacteria into the system after the water change to keep ammonia levels down.


For the full two weeks, we feed the fish medicated foods. For two cubes of frozen food, we add the following.

  • 1 scoop of metroplex
  • 1 scoop of kanaplex
  • 1 scoop of praziquantel (powder form, not prazipro)
  • 3 scoops of seachem focus

Let this blend sit for at least 30 minutes, then feed to your fish. If you are having trouble getting the praziquantel to dissolve, DMSO or vodka can be added to help it dissolve.

Keep the leftovers in the refrigerator.

We feed twice per day while in QT (unless the fish has very high metabolism and requires more frequent feedings).

When am I done?

If you have seen no visible symptoms of disease for 14 days, then you are finished treating, and the fish is ready to be added to your display. As a final step, we like to "rinse" the fish in some freshly mixed water / water pulled from the display for a few minutes, just to get the medicated water out of the fish's gills.

Though this sounds like a lot (and it is definitely not effortless), it is a great way to bond with your fish before getting them into the display. This is also an involved method of QT, and may be better suited for those with less patience.

About us

Thank you very much for reading! If you have any questions, feel free to reach out to us directly. If you found this post useful, we hope you will consider sharing it with others. We also invite you to sign up for our mailing list, where you will be notified when we add new blog posts and add new corals to the store.

We also hope you will consider us for your future coral purchases!

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