Medications Needed for Treating Marine Fish Diseases in Quarantine

Now that you have decided to quarantine your fish, 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 without causing too much additional stress during treatment (I do this with all my new fish).

Treating fish regardless of them showing symptoms may raise a few eyebrows, as medication causes stress in fish. However, treating all new fish can save you time and also give you peace of mind that your new fish are 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 – in general, most healthy fish will be able to tolerate medications quite well. If you have a particularly sensitive fish, or perhaps a fish that is not feeding after acclimatisation, it may be wise to observe the fish for a few days without medication in a quarantine tank. To reduce stress on the new fish, ensure water parameters are excellent and consistent. Try providing food with garlic to encourage feeding, and once your fish has began to eat, you may consider beginning a medication regimen.

I always prophylactically treat my 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. I assume my fish are likely sick and treat right away.

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.

Once you’ve bought your fish and are home getting ready to acclimatise it, spend a few minutes taking a look at the fish closely under light. Try to see if you can spot any items listed below.

Obvious symptoms of sick fish include:

  • Loss of appetite (after acclimatisation
  • Rapid or heavy breathing (This is usually serious – your fish might not make it)
  • Bulging /’pop-eyes’
  • Sores on the body
  • Damaged / disintegrated fins (fin rot)
  • Red / inflamed scales or fins
  • Extreme lethargy
  • Bloating in the abdomen

More subtle / early symptoms of fish illnesses include:

  • Loss of appetite
  • Loss of color
  • Lethargy
  • Fish looks a little out of breath

If your fish has any of the above symptoms but will feed, you should begin treatment right away. If you 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. I usually find more success when I 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 favourite) which are highly effective treatments.

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

Personally, I always use SeaChem’s Kanaplex as part of a medicated quarantine treatment with great success (high fish tolerance, and so far no incidence of disease after treatment)

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 treat your fish in a quarantine or hospital tank, and not your main or display tank. Antibiotics can also wreak havoc on corals and invertebrates, so don’t use this on your display tank!

In my experience, I have found that Kanaplex does not affect the biological filter much at all, whilst curing all fish from bacterial infection in a quarantine setting. If you are worried that your biological filter being affected, you can always re-seed it with some 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 aanthelmintic 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 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.

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 manufacturers 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.

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 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. You can use this medication as an alternative to using cupramine and prazipro. I have not used paraguard myself, but I have heard 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 >>