Fish Antibiotics and Other Aquarium Medications

Fish Antibiotics and Other Aquarium Medications

One question that came up recently for a friend of mine (and newsletter subscriber) was what to do about two fish that had cloudy eyes. The person was already using one popular product and wasn’t seeing any improvement, and they wanted to know what product I would recommend they should try next.
Unfortunately, this friend’s dilemma (which will hopefully turn around for them soon), was the inspiration for this blog post.
I knew they should try  fish antibiotics, but rather than just tell them about the last fish antibiotic I purchased, I wanted to refer them to a trusted source to help him troubleshoot his problem and find the perfect therapy, but I didn’t know where to send him. So I did some homework, the same way I would if I was having the problem myself. What I found was a staggering list of available fish antibiotics products and thought to myself…how in the world are we supposed to figure this out? Physicians and veterinarians go to school for years to learn how to properly diagnose and treat diseases. I am not a fish doctor, and I don’t play one on TV, but I do try to be helpful, when I can. Some of this I knew and wrote without research, some of it I knew but it wasn’t top of mind and some of it I learned for the first time.

fish antibiotics

There are a few types of medications available for the marine aquarium including the fish antibiotics:

  • Alternative medicines or “natural” remedies
  • Slime coat enhancers
  • Fish Antibiotics
  • Antifungals

Alternative medicines or “natural” remedies

One of the places many marine aquarium hobbyists look first is for a natural remedy. Some people are inclined to think that natural remedies are better than chemical or pharmaceutical remedies. The good news is that if you are one of these people, there are lots of products available for you. The bad news is that many of these products are unproven, at least as far as I can tell.

Garlic-containing products

You may get hungry when you smell garlic bread roasting in your oven, but do your fish? It may seem plausible that garlic-containing natural remedy promotes feeding in finicky fish, but where is the evidence? Furthermore, is there any evidence that stimulating fish to eat does anything more for them other than put calories in their body now rather than 5 minutes from now? What is the benefit of that?

Slime coat enhancers

Another group of the so-called “natural” remedies are a group of products I’m going to call…the slime coat enhancers. Not the most appetizing names I’ve ever seen, but it is descriptive, I suppose. If you look at the ingredients label of a slime coat enhancing product, you may wonder why I chose to call it a natural product? I think I categorize them in the “natural” bucket because they don’t act on the bacteria, fungus or parasite causing the problem, they enhance the production of the slime coat, which is one of the fish’s natural lines of defense against intruders.

not a fish antibiotic

The premise, from a marketing perspective, is somewhat compelling…fish do have a slime coat that acts as a natural barrier and helps prevent infection, so it seems like a good idea, on the surface, to add something to the water to help promote that, but the thing I never understood about the slime coat enhancers is how this actually works. For example, if you had a cold, and I gave you a product that was going to help enhance the production of the slime coat in your nose (ie. your buggers…hehehe…I’ve been waiting for a long time to put that word in an article), the effect there would be a runny nose, which is also one of your body’s natural defenses to an invader–but if you suspect you’re already sick, would giving you a runny (or runnier, if already runny) nose make you feel better or otherwise help you heal better? I’m not so sure. In fact, I know that I hate a runny, stuffy nose, and I generally take a medication to make my nose less runny, whenever I can. Call me a skeptic, but I’m not quite convinced.

Products touting natural extracts

  • Melafix is a natural antibacterial remedy with Tea Tree extract to treat bacterial infections. Heals wounds, ulcers and removes parasitic flatforms
  • PrimaFix is a natural antifungal and antibacterial remedy with West Indian Bay Tree extract to treat fungal infections and external bacterial infections.

Fish Antibiotics

Fish Antibiotics are a group of powerful drugs that fight bacterial infections–usually by killing the bacteria or at least keeping them from growing (which helps achieve the same outcome). No doubt about it or hesitation in my characterization here, because many of the antibiotics available for fish are or were also available for human use with a prescription and medicines for human use undergo extensive research in clinical trials with animals (probably mice and rats, not fish or corals) and humans. The following drugs are fish antibiotics for aquarium use without a prescription:

  • Penicillin
  • Ampicillin
  • Amoxicillin
  • Cephalexin
  • Clindamycin
  • Ciprofloxacin
  • Erythromycin (Maracyn)
  • Neomycin
  • Kanamycin
  • Tetracycline
  • Minocycline (Maracyn-2)
  • Trimethoprin and Sulfonamide (Maracyn Plus)
  • Sulfamethoxazole/Trimethoprim
  • Nitrofurazone
  • Furazolidone
  • Sodium sulfathiazole, sodium sulfamethazine and sodium sulfacetamide are three antibiotics that are sold together under the name Triple Sulfa for combatting bacterial infections


The big issue here is: how do you pick the right fish antibiotic from this dizzying list of hard to pronounce options? The scary thing is that some of these products are not even suited for use in a marine aquarium. Tetracycline isn’t effective in saltwater and penicillin, ampicillin and amoxicillin aren’t that effective in fish, despite the fact that they are available as a non-prescription fish antibiotic (source). A little further down the page, I will give you my recommendation, but for now, let’s take a look at the next group of treatments for a sick fish.

Fish Antifungals

Antifungal medications, as you might have guessed, are drugs that fight fungus…er…funguses..I mean fungii.
Fungal infections quite often look like white fuzz or cotton. If you suspect your fish have a fungal infection, you can treat it with an anti-fungal agent like Fungus Cure or Maracyn Oxy.   A good number of helpful drugs, like Maracyn Plus or Melafix have both antibacterial and anti fungal properties, which is good, because a lot of fungal infections take place after an initial injury and bacterial infection.

 treats fungal fish disease

Marine Aquarium Fish Diseases and Treatments

So which treatment should you choose? I’m not a fish doctor, and I’m not trying to play one here. I encourage you to do more research and double-check the info I’m posting here, for your background, but here are some recommendations I believe to be sound. Five products that can be used to treat a range of infections are:

Fungal infections

Consider treating cotton-mouth fungal infections with MelafixMaracyn 2 or Furan-2.

Cloudy eyes and Popeye

Consider treating cloudy eyes and popeye with the fish antibiotics Melafix, or Triple Sulfa

Fin and tail rot

Consider treating fin and tail rot with fish antibiotics like Maracyn 2, erythromycin, Melafix, Triple Sulfa or Furan-2

Parastitic infestations

If the problem you are facing is from parasites, like saltwater ich, flukes, anchor worms, or marine velvet, consider using hyposalinity (free) or copper/cupramine

Some general advice

  • Whenever possible, try to remove a sick or injured fish to a hospital tank, where you can medicate them in isolation and observe them during the treatment. You don’t want to risk harming the healthy fish in your display tank by accident.
  • Watch out for ‘old fish antibiotics’. Check the expiration date to make sure it’s going to work.
  • Read the dosing instructions that come with your fish antibiotics and be careful to make sure you dose the product as directed–including performing water changes as directed.
  • Don’t overlook the importance of having high quality, clean water parameters and adequate nutrition in helping your fish fight off infection with their own immune system.

For more information

For more information about fish diseases and treatments, including where and when to use fish antibiotics, check out the following resources:
Pictorial fish disease guide
American Aquarium Products website, one of the major manufacturers of fish antibiotics
To learn more about creating and maintaining a thriving aquarium, check out:


  1. What about intestinal worms? What can we use to treat that?

  2. Author

    Hi Dan, thanks for the great question (and a tough question it is). Treating internal parasites (intestinal worms) is tough for a few reasons. 1) it is tough to diagnose and 2) if you do diagnose, it is tough to treat. The best source I found on this topic and recommend is The Salt Smart Guide to Preventing, Diagnosing and Treating Diseases of Marine Fishes by Jay Hemdal.

    If you are talking about a tape worm, the advice is to let it die out. If you’re talking about other internal worms, the recommendation is medicated foods–but they are dosed by weight…and how do you know what your fish weighs? Hemdal reports anecdotal evidence that praziquantel,INTERCEPTOR or PRAZIPRO dosed at 2.2 to 4 mg/L.The problem with that is that the parasites are in the gut…and dosing the water is a very bad way to get medicine into a fish’s gut.

    Garlic is a common remedy–Hemdal is somewhat positive about it as a therapy and irritant. I’m a bit skeptical of that but haven’t seen the data. I hope that helps.

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