Melafix, side effects, Overdose and Uses

Last Updated on December 18, 2021 by cmoarz

Mealafix is a general antibiotic used to treat aquarium fish for various bacterial infections and bacterial growth. Although technically it isn’t an “antibiotic”, the main ingredient, Melaleuca, has antibacterial properties. 1.0% Melaleuca (Cajeput or ‘Tea Tree’ Oil) is in Melafix.

Warning: Not to be confused with Melafix Pond which contains a whopping 5.0% Melaleuca. This is 4x higher than an aquarium dose and should not be used in your aquarium. Always double-check your labels and dosage!

If this is the first time you’ve medicated your aquarium, Or used API Melafix, and you are worried about overdosing and side effects, and how it could adversely affect your other fish, this article will give you all the information you need to make an informed decision on whether this product is right for you and your pet fish.

Possible side effects

Melafix has very few potential side effects. Overdose is possible if you go over the recommended dose of 5ml per 10 U.S gallons.

In case of overdose, Quickly do a large water change multiple times with clean water to remove the excess melaleuca extract. Continue treatment with a melaleuca liquid (Melafix) dose daily every day for 7 days.

Some side effects include a large amount of foaming on the surface of the water such as you would see during an ammonia spike or poor water quality. This is normal if you have a bubbler or a filter that creates water turbulence.

Generally, it’s considered being safe for most fish, such as clown loaches, discus fry, tetras, guppies, etc.

Human consumption of melafix should be avoided, and should not be used on any fish intended for human consumption. Human consumption of Melaleuca liquid has been shown to cause birth defects in humans and can be a harm.

Use for sick fish only. Not for use in persons or food stock.

What to watch for when using Pimafix and Melafix

There isn’t much to watch for if you are using these safe products other than the standard things. Some of the melafix overdose symptoms include:

  • Are your fish acting strangely in any way?
  • Are they behaving more erratic than usual?
  • Do they stay at the top of the water or appear to be gasping to air, Or otherwise uncomfortable since the addition of the melafix?
  • Seizures

If your fish generally act out of the norm, and it isn’t related to the initial disease symptoms or bacterial diseases then you should do a large water change asap to dilute the Melafix or Primafix.

Will Melafix hurt healthy fish

No, Melafix (melaleuca liquid) is perfectly safe for most healthy fish. Feel free to use it in your aquarium for 1 sick fish as it won’t affect the others. Be aware of what you have in your community tanks however to be sure the other fish won’t have any adverse effects, such as labyrinth fish.

If you’ve got an undesirable mix of community fish, Consider setting up a quarantine tank for medicating.

Are Melafix and Primafix safe for labyrinth fish like betta fish?

People claim to have had issues with other passive medication API products such as Melafix and Primafix on fish that contain a labyrinth organ to breathe with.

As far as we’re concerned, these Claims are partially true. Some fish have had their labyrinth organ affected by Melafix and Primafix because of the thin layer of film over the water’s surface and other complex interactions, including a similar burning of the lungs that happens in humans, causing these fish to drown.

A better alternative for labyrinth fish is bettafix. It’s much the same but with 1/10th the amount of active ingredient.

The option of just using salt is also just as effective as bettafix with less harm, but won’t be possible in a tank with snails or shrimp.

What about crustaceans and mollusks and snails?

Melafix, Primafix, and the combination thereof are perfectly fine for use with snails and shrimp and other crustaceans and mollusks in the tank.

Does Primafix or Melafix kill beneficial bacteria? It’s also important to note that these chemicals won’t hurt the biological bacteria in the biological filter or any other microorganisms. Corals are also unaffected.

Aquarium salt however should be avoided as an alternative when snails, shrimp, or other salt-sensitive creatures are in the tank. Api Melafix and API Primafix contain no salt as an ingredient.

What is Melafix and Primafix used for?


As stated above, This chemical is an emulsified oil and water used to treat bacterial infections. Its main active ingredient is Tea tree oil. At this time, it is not FDA approved and you do not need a prescription to purchase it. Melafix targets gram-positive and gram-negative and other bacteria.

It’s primarily used for wound treatment in marine fish as a preventative to bacterial infections in such circumstances as open wounds, tail rot, torn fins, infection, etc. It’s also commonly used in quarantine tanks before adding new fish to the main tank.

Melafix can be used in saltwater aquariums and freshwater aquariums without issue as an all-natural antibacterial treatment. It will not hurt your aquarium plants, although it does have a somewhat medicated unpleasant odor. It will also cause a foam on top of the water if you have a bubbler/airstone as it creates a thin layer over the surface of the water which air gets trapped inside.

Normally this is something you would see with an ammonia spike or very dirty water, Luckily that isn’t the case here.

Activated carbon will remove it from the water, So it’s advised you remove any activated carbon filter media if you intend on dosing your tank with Melafix.


Primafix is much like Melafix but as an anti-fungal agent used to treat mouth fungus. Unlike Melafix that uses tea tree oil, Primafix uses Pimenta racemosa emulsified with water. It will treat fungus infections, cottony growth, mouth fungus, and other sorts of fungus-related issues. They can be safely mixed together which is super nice when used in an isolation tank before adding fish to the main tank.

Can it be used for treating ich?

Unfortunately, Melafix won’t fix ich. However, It will do a wonderful job at preventing and treating secondary infections from the wounds the ich parasites leave behind as well as scratches on the fish’ skin from “itching” on rocks and decorations.

Melafix should not be mixed with ich treatments and will require several large water changes and at least 7 days after the ichs’ last medication dose before it’s safe to use melafix again in the tank.

A better treatment for ich is to increase the temperature and addition of aquarium salts. Doses for this are out of scope for this article as it’s a complicated topic and each fish has its own unique needs.

Can it be used for fin rot?

Since fin rot is one of many bacterial diseases, API Melafix is excellent at treating, and healing bacterial infections that cause fin and tail rot, and body slime.

It also acts as a very good preventative measure when a fish has a wound or scratch.

Can I use Melafix with other treatments?

API Melafix (anti-bacterial), Primafix (anti-fungal), and other API products such as conditioners can all be used in combination and in conjunction with each other.

It’s important to note that some medications can interact with these products, as well as salt and heat. Due diligence is required to figure out what combination of what can be safe for your aquarium and whether it will cause harm to the fishes.


Owner of and also owner of actual Aquarium Gravel believe it or not! ;). Setting up beautiful aquarium sceneries and habitats since I was very young. Enjoy!