Medications for Treating Marine Fish Diseases in Quarantine

Now that you have made the prudent and wise decision to quarantine your fish (read up on reasons why to quarantine your fish here) and have set up your quarantine tank,  you need to decide if you will treat your fish prophylactically (before symptoms) or when and if symptoms appear.

If you have more time on your hands, you may choose to observe your fish and only treat them should they become sick. The other option is to prophylactically treat your fish, hopefully, before disease sets in and your fish becomes too sick to eat or recover. We treat our fish with our easy quarantine method once they are acclimatized in our quarantine tank as we know our local fish store does not practice good fishkeeping standards – all the different fish tanks share the same water filter system, meaning there is high risk of disease transmission.

There is much debate on treating right away vs. treating only when disease symptoms appear with rational arguments on both sides. For example, there is a risk that a healthy fish that may just need some rest from the journey from his habitat to the fish store to your tank may just need a few days to recover in a quarantine tank before he will start eating. Then others rightfully also point out that those precious few days could have been used to start treatment early and potentially save the fish’s life, especially if it has a disease that progresses rapidly. There is no correct answer, however, we opt on the safe side and always provide a standard treatment regime for all our new fish regardless of their behavior or appearance once they enter the quarantine tank.

Treating fish regardless of them showing symptoms may raise a few eyebrows, as medication does cause some stress in fish. However, treating all new fish can save you time and also give you peace of mind that once they complete quarantine, your new fish are pretty certain to be disease free and won’t infect other fish in your display tank.

A well prepared quarantine tank – HOB filter, Heater, Ammonia Alert, Food, Prazipro & Cupramine

Rest assured as in general, most healthy fish will be able to tolerate medications quite well. This is because a lot of newer medications such as Paraguard or Cupramine from Seachem have been formulated to reduce stress on fish while maintaining the effectiveness of the active ingredients. If you have a particularly sensitive species fish, or perhaps a fish that is not feeding after acclimatization, it is still sensible to observe the fish for a day or two without medication in a quarantine tank, in the hopes they will start eating. To reduce stress on the new fish, ensure water parameters are excellent and consistent and the fish has been acclimatised correctly. If your fish is not eating, try providing food with garlic or some live Mysis shrimp dipped in Garlic Guard from Seachem to encourage feeding. Once your fish has begun to eat, you may consider beginning a medication regimen. If your fish is not eating after 1 day in the quarantine tank, then you will need to decide what to do. Sometimes disease has started to take hold and more gentle medicines may help him recover slightly to begin feeding. The odds of getting a non-eating fish to recover to a state where it will start to feed is about 60/40 in your favor.

We always prophylactically treat our fish, even if they don’t show any symptoms. This just saves time as I don’t have to wait for symptoms to appear before beginning treatment. We assume my fish are likely sick and treated right away because we are familiar with the way fish are transported and stored at our local fish stores. Fish stores near us import fish in bulk and all their holding tanks share the same water, so it is likely many fish are sick / carrying diseases.

Most accepted preventative quarantine treatments include:

  • Treatment for bacterial infections (bloated fish, bloody patches, pop-eye)
A fish with pop-eye. Fish that have both eyes popped out likely indicates a bacterial infection.
  • Treatment for external parasites (Ich, Brooklynella, Marine Velvet)
Marine Ich can be easily identified by the white, salt grain sized dots that pepper the skin of the fish.
  • Treatment for internal parasites (gill flukes, worms)
Marine flukes can be hard to spot, but are also relatively easy to treat.

Can’t figure out which disease your fish might have? Check out this handy chart from Seachem.

Before bringing your fish home, take some time to study it under light at the fish store. Make sure it is not breathing rapidly and it is preferable if you can confirm it is eating at the fish store. Once you’ve decided to bring your new fish home, when you are getting ready to acclimatize it, spend a few minutes taking a look at the fish in it’s bag closely under a light. Try to see if you can spot any items listed below.

Obvious symptoms of sick fish include:

  • Loss of appetite (after acclimatization)
  • Spots on skin
  • Rapid or heavy breathing (This is usually serious – you need to start treatment ASAP)
  • Bulging / cloudy / ‘popped-eyes’
  • Red sores on the body (hemorrhaging) 
  • Damaged / ragged / disintegrated fins (fin rot)
  • Red/inflamed scales or fins
  • Extreme lethargy
  • Inability to maintain or control buoyancy. 
  • Bloating in the abdomen

More subtle / early symptoms of fish illnesses include:

  • Loss of appetite
  • Loss of color
  • Skittishness/ jumpiness / darting around tank
  • Lethargy
  • Fish looks a little out of breath / fast fanning pectoral fins while resting.

If your fish has any of the above symptoms but will feed, you should begin treatment within a few hours. For general malaise, try giving the fish a day to calm down and get used to the quarantine tank. Make sure your quarantine tank is set up correctly, with hiding places and proper temperature control .  Try to feed the fish as much as it can eat during this time (but do not leave any discarded food in the water). If your fish doesn’t feed and seems weak, you have to make a tough decision. You can keep it in quarantine with excellent water parameters and hope it gains enough strength to start feeding, or you can begin treatment in the hope you can stop the disease from progressing further to allow your fish to begin recovery. We usually find more success when we begin treatment as soon as possible.

Marine Fish Medications


My personal favourite – Kanaplex is effective but gentle, and also does not affect the biological filter.

You won’t be able to determine which bacteria is causing an infection in your fish, therefore, it is essential that the prescribed treatment is broad enough to target the usual suspects found in marine fish.

Some treatments such as the erythromycin based Maracyn-2, target gram-negative bacteria, which are the most common type in marine fish infections. However, you could use a broad-spectrum antibiotic such as products containing neomycin, chloramphenicol, nitrofurazone, or the skin-absorbed kanamycin sulfate (Kanacyn/K-Mycin, Kanaplex is my personal favorite) which are highly effective treatments. You may also consider simultaneously dosing Metroplex with Kanaplex to cover all your bases when it comes to fish infections (Metroplex works against parasites, Kanaplex against bacterial infections). If your fish is feeding you should also consider mixing in some Seachem Focus with the Kanaplex and a little food. This will help the fish ingest the antibiotic for greater effectiveness. 

An ultra-broad spectrum antibiotic blend of nitrofurazone and kanamycin called Spectrogram is available should other antibiotic medications fail to work.

Personally, we always have SeaChem’s Kanaplex on hand as part of a medicated quarantine treatment should any fish not feed within a few days. We have had great success (high fish tolerance, and so far no incidence of disease after treatment) with this approach. Additionally, we mix small amounts of kanaplex / metroplex with Focus from Seachem to ensure that some of the antibiotics are ingested during feeding once they start eating again.

Remember, as with people, antibiotic resistance can develop in fish. Repeat exposure to medication and incomplete courses of antibiotics can breed resistant strains of bacteria. The use of a strong, broad-spectrum antibiotic in accordance with the manufacturer’s instructions will likely kill off all harmful bacteria in the first go.

The downside to treating your fish with antibiotics, especially a broad-spectrum one, is that it may also kill off some bacteria in your biological filter.  It is for this reason that it is recommended that you only treat your fish in a quarantine or hospital tank, and not your main or display tank. This way you can replace the filter media after treatment and ensure there is still some biological filtration occurring in your quarantine tank. Antibiotics can also wreak havoc on corals and invertebrates, so do not use this on your display tank!

In our experience, we have found that Kanaplex does not affect the biological filter much at all, while also curing all fish from bacterial infections in a quarantine tank setting. If you are worried that your biological filter is affected, you can always re-seed it with some new filter media from your main tank, Seachem Stability, or other biological de-nitrifying bacteria starter after the treatment is complete.

Prazipro (Praziquantel)

Prazipro – a gentle and effective medication for flukes and parasites.

Prazipro, an anthelmintic or deworming medication that works by paralyzing worms and flukes with little side effect on the fish itself. Prazipro is considered to be a relatively gentle medication and if used correctly, is a safe and effective way to remove flukes and worms from fish in a quarantine setting. This medication (like most, if not all medications) should not be used in your display or main tank – reason being there are likely a few species of worm in your tank (either in the sand or live rock) that may be sensitive to this medication.

Copper / (Cupramine)

Cupramine, a popular copper based medicine is essential when quarantining new fish, but is toxic to inverts.

Cupramine (Buffered Active Copper) is a copper treatment manufactured by Seachem. It is a safe and much more forgiving alternative to other copper medications (notably copper chloride, sulphate and citrate), as the copper is bound to an amine which reduces it’s toxicity in fish. We use cupramine to treat all our fish prophylactically (regardless on if they are showing signs of disease), in our easy quarantine method for marine fish.

Cupramine treats a wide range of ailments in fish, including Amyloodinium / Oodinium (Marine Velvet), Ichthyophthirius  / Cryptocaryon (Saltwater Ich), gill flukes, and other external parasites. Copper is toxic to these parasites when they are in the free swimming stage, thus stopping their lifecycle. It because the medication only affects free swimmer stages (as opposed to the encysted stages of these parasites) that you need to treat fish over a minimum of a few weeks to ensure it kills all of the parasites.

While treating with copper based medications, it is important that you obtain a copper test kit to measure the copper levels in your quarantine tank as levels above the manufacturer’s instructions are toxic to many fish. Salifert, again, produces a copper test with high sensitivity with an easy-to-read coloration scale that tells you precisely how much copper you have. Don’t skimp and get a cheaper copper test kit – it can mean life or death for your fish when treating with copper. Do not mix copper based medications with Seachem’s Paraguard or Prime as they can negatively increase your fish’s sensitivity to the medications.

Copper medications have a tendency to be absorbed by many aquarium surfaces, such as rocks, sand, silicone and filter media. It is for this reason that you should not use copper in your display tank, even if you are running a fish only with live rock (FOWLR) tank, as if you change your mind in the future, copper traces may still be a problem. Copper residues and the sensitivity of copper in invertebrates means that you will have to clean your quarantine tank thoroughly after using copper-based medications should you wish to quarantine inverts. If you plan to add fish, corals and inverts regularly to your tank, it may be easier and safer to have one tank and set of equipment for inverts, and another for fish.


Paraguard is filter-safe, aldehyde-based medication used to treat ich, velvet, fin-rot and flukes. It is what can be considered to be a “preventative” medication meaning it may prevent other fish in your quarantine tank from getting sick from a fish that is carrying disease. Paraguard can be used once your fish have started to eat as we found that it is an effective and gentle medication that can be used to treat fish prophylactically.

Next: Once you have these medications, and your quarantine tank set up, you’re ready to begin the quarantine process >>