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Will Melafix Hurt Healthy Fish?

With Melafix being one of the most popular treatment options for a wide range of common issues in fish, we see a number of questions being asked about the treatment each month as people turn to it to help their own fish through various problems.

One of the more common questions we have seen people asking about recently is if Melafix will hurt the healthy fish in their aquarium or not.

Although this may sound as though it should be a clear yes or no answer, it really isn’t and there are a number of different variables that you have to factor in.

Our regular readers will know that we are huge fans of Melafix and often recommended it for treating your fish but as we have covered in a few articles such as our article on if Melafix works as well as our ultimate Pimafix vs Melafix comparison, you really do have to factor a number of factors in when using Melafix in your tank.

We see a number of slightly different questions each month about using Melafix in your tank and its effects on the healthy fish in your tank so we wanted to try and answer them all in this article to create somewhat of an ultimate resource.

Will Melafix Hurt Healthy Fish?

Melafix can cause some issues with more sensitive fish and it is usually recommended that you try to quarantine a sick fish if possible when treating it with Melafix.

These issues that can occur on your healthy fish range from inflammation of their gills to reddening of their eyes.

In some situations, it can be advantageous to treat your healthy fish with Melafix though as conditions such as fin or tail rot can quickly spread to fish that currently look healthy.

As we covered in our article on using Melafix for Betta fish, Melafix is not the best option for all fish species and we would always recommend that you use Bettafix for betta fish instead of Melafix if possible.

There are a number of other fish species that can have issues with Melafix too but the majority of the more popular fish, especially freshwater fish but this is a trade off.

Many of the conditions that Melafix is used to treat such as tail rot, fin rot, dropsy, and mouth fungus can rapidly spread between the fish in your tank.

Many fish keepers will simply choose to treat their full tank rather than a single fish as a fish that seems healthy right now may have the same condition you are treating in another fish with the seemingly healthy fish just being at the starting stages so you will probably have to treat it with Melafix in the future anyway.

Why Do People Quarantine Fish When Treating Them With Melafix?

The three main reasons people quarantine sick fish when treating them with Melafix is to try and stop the condition from spreading to healthy fish, protect healthy fish from potential side effects of Melafix, and to protect sensitive live plants, corals, and anemones in their tanks.

Unfortunately, some fish species don’t do well with the process of being caught and quarantined in a separate tank so some types of fish will have to stay in their main tank.

If you are keeping saltwater fish and do have sensitive plants, corals, and anemones in the tank then it really can be a pain to treat some issues as Melafix can cause issues with those tank mates.

To make the situation worse, it is usually the saltwater fish species like blue tang who tend to not do well in quarantine due to the catching process of being chased around their home by a net stressing them out and making them anxious.

The majority of our readers do keep freshwater fish though and this makes it much easier to catch and quarantine a fish if you do choose to take this patch.

On top of this, many of our readers keep very small fresh water fish such as guppies too so if you don’t have a spare tank to use for quarantine, you can often use some clean household items that hold water for the quarantine phase too.

Does Melafix Kill Beneficial Bacteria?

Melafix uses tea tree extract as its active ingredient and it will kill all types of bacteria in your tank including the beneficial bacterial.

You are usually able to purchase cultures of various beneficial bacteria online to re-stock your tank with them after treating the tank with Melafix if you wish.

The vast majority of fish keepers will usually be ok with the beneficial bacteria in their tank being displeased if it is able to save their fish though.

Some types of intentionally kept algaes such as coralline algae can also have issues if they are in a tank that has been tret with Melafix too.

Melafix does usually have the stronger active ingredient so depending on what you are doing with your tank, trying Pimafix may be a valid workaround.

Pimafix can treat many of the same conditions as Melafix but its active ingredient is West Indian bay tree extract and it is slightly weaker against bacteria when compared to the tea tree extract used in Melafix.


That brings our article going over if Melafix will hurt healthy fish or not to an end. We hope that we have been able to help you better understand how Melafix can be a double edged sword for your healthy fish in your tank depending on the situation. Many fish keepers do just choose to treat the full tank though as many conditions that require Melafix to treat them can quickly spread to other fish in the tank meaning those fish will also need treating in the future anyway.