fish antibiotics and other aquarium medications

Fish antibiotics: learn which one is best to treat your sick fish

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 fish antibiotics they should get to clear up the symptoms.

Unfortunately, this friend’s dilemma (which will hopefully turn around for them soon), was the inspiration for this blog post.

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 antibiotic 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.

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

Fish Antibiotics

Fish Antibiotics are a group of powerful drugs that fight bacteria and the infections they cause. They typically work by killing the bacteria or at least keeping them from growing (which helps achieve the same outcome, since they eventually die).

When I think about antibiotics, my mind drifts to all the trips to the doctor’s office, over the years. Today, the doctor’s office tends to send the prescription electronically to the pharmacy, where it is ready for pick up by the time I get there, ideally. A pretty big improvement in terms of convenience.

Well, if your fish is sick, it’s even more convenient, because fish antibiotics are not restricted and regulated by the United States Food and Drug Administration, or FDA for short, in the same way, that the prescriptions are for humans. You can get your fish meds at any pet store with a reasonable selection of aquarium dry goods the same way you can get food and filter materials. Pretty cool, and convenient.

16 Best fish antibiotics and alternatives for saltwater fish:

  1. Ampicillin
  2. Amoxicillin
  3. Cephalexin
  4. Clindamycin
  5. Ciprofloxacin
  6. Erythromycin (Maracyn)
  7. Neomycin
  8. Kanamycin
  9. Penicillin
  10. Tetracycline
  11. Minocycline (Maracyn-2)
  12. Trimethoprin and Sulfonamide (Maracyn Plus)
  13. Sulfamethoxazole/Trimethoprim
  14. Nitrofurazone
  15. Furazolidone
  16. Sodium sulfathiazole, sodium sulfamethazine, and sodium sulfacetamide are three antibiotics that are sold together under the name Triple Sulfa for combatting bacterial infections

A few fish antibiotic complications to sort through

There are only two small complications to sort through when you are at the local fish store.

1. They all have funny names, which medication is it?

The first thing is–how can you tell which medication is which, with all the trade names. The key is to take a moment to look read the packaging to figure out which medication it is. Some of the products made by Thomas Labs are easier to figure out than some others. For example, FISH PEN is Penicillin, FISH CILLIN is Ampicillin. FISH MOX is Amoxicillin, FISH FLOX is ciprofloxacin, FISH ZOLE is Metronidazole, FISH FLEX is Cephalexin, and so on. It gets complicated with some of the medications like MARACYN, erythromycin or MARACYN TWO (which is minocycline…go figure)

2. Which medication is right for my fish?

The second big issue is–how do you know what medication is the right one for the symptoms or disease your fish has? That’s a bit tricky. Don’t forget, doctors, including veterinarians, go to medical school for a very long time to become experts in this field–and it’s not hard to imagine that even they get it wrong sometimes.

So don’t stress about it, just do your best, and see below for some more specific advice on matching the symptoms or disease with the right fish meds.

3. A Conflict of Interest?

Interestingly, it seems like fish antibiotics are marketed more towards people trying to buy for human use (or stockpiling), more than for the fish themselves. Which is disturbing, and I suspect, illegal.

If you’ll indulge my train of thought here–I do see the point–somewhat. Survivalists, preppers and even people who don’t necessarily fall into those stereotypical buckets want to have supplies on-hand in case something bad happens. You certainly can’t blame them, and based on regulations, they are not allowed to buy the versions intended for human consumption. So if they are motivated to try and keep these life-saving supplies on-hand, this is their only choice.

There are also likely individuals who believe they would benefit from taking the medication but don’t want to visit their doctor, for a few reasons, I’m sure. What options do they have?

If you found this page because you’re looking for information about whether or not they are safe and effective for human consumption, I am sorry to disappoint. That’s not the point of this article, I’m actually interested in the fish…surprisingly :). Don’t judge us fish geeks and we won’t judge you, survivalists 🙂

4. Buyer beware

caveat emptor, means buyer beware in Latin

You do have to be careful, though. Just because you can buy a product at the pet store, doesn’t mean it’s suited for a marine aquarium. Clearly, some of these products are not.

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 fungi.
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 antifungal properties, which is good because a lot of fungal infections take place after an initial injury and bacterial infection.

 treats fungal fish disease

Alternative medicines or “natural” remedies

One of the places many marine aquarium hobbyists turn first is to look 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?

For what it is worth, I’m going to need to see some better data (any data?) from the BIG GARLIC COALITION before I would be willing to endorse or advocate here.

garlic is sometimes used as an aquarium remedy
Get it…big garlic?

Slime coat enhancers

Another group of the so-called “natural” remedies is 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 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.

Copper-based medications

One of the most battle-tested and proven remedies for dealing with external parasites are the copper-based medications–specifically, cupramine, which is the preferred version of copper that you want to add to a saltwater tank. It is generally thought to be better than medications with copper sulfate, and those with chelates, for saltwater applications.

Copper is notoriously unstable in saltwater, which means that the medication you put in the water to cure your fish keeps breaking down, over time. When it breaks down, there is less and less medication in the water, and eventually, there won’t be enough to cure your fish. Because of this, manufacturers have come up with other ways to make the copper more stable, like adding chelates, but this diminishes the effectiveness of the treatment.

cupramine is the best copper-based medication for saltwater fish

I know, that’s a lot of chemistry and big words there. Bottom line, go for cupramine.

An important safety warning with copper

Copper is used as an aquarium medication because it is good at killing things. The technical term is that it is toxic. At the therapeutic dose (meaning when you have the right amount of it in the water to kill the parasites), it will also kill any other invertebrates in the water–that means your shrimp, clams, corals, crabs, copepods, amphipods, mysis shrimp, pretty much anything in your tank that you cherish will also be killed.

So never, never, never add copper directly to your display tank. You have to use copper in a separate tank. At dose levels above the therapeutic dose (meaning when the concentration gets significantly higher than what you need to kill the parasites), copper can be lethal to your fish, too.

quarantine tank setup

So now, let’s summarize a few of these important points about copper-based medications:

  • Copper will kill all the invertebrates in your tank and could hurt your fish too if you’re not careful
  • Copper levels will continually get weaker, over time
  • You have to keep adding copper to keep it at the therapeutical level
  • Levels below the therapeutic level won’t work
  • Levels above the therapeutical level my kill your fish

The solution: You need to use a copper test kit to test the water in your quarantine tank to determine the level and calculate how much copper to add. Not too much, not too little, but just right.

Copper-based medications are effective but complicated.

Here are the five most important fish meds that can be used to treat a range of infections, symptoms, and conditions:

A quick guide to matching up the saltwater fish symptoms to the right medication

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.

Fungal infections

Consider treating cotton-mouth fungal infections with Melafix, Maracyn 2, SulfaPlex or Furan-2.

Cloudy eyes and Popeye

Consider treating cloudy eyes and Popeye with  Melafix, or SulfaPlex

Fin and tail rot

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

Parasitic infestations

If the problem you are facing is from parasites, like saltwater ich, flukes, anchor worms, or marine velvet, consider using hyposalinity (free) or 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 these fish meds 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.

Ready to check out prices online?

If you are looking to buy fish meds online, or even just check out prices, please take a look at They offer free shipping, and if you order from Amazon after using any of the links on this page, they will provide support to me and this website, at no additional cost to you.

Buy fish antibiotics and other meds online at Amazon

fish antibiotics and other aquarium medications







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