Melafix (and Pimafix) are both natural treatments (Melafix is made from tea tree oils). The melafix is a bacterial infection treatment, while pimafix is used to treat fungal infections. I always recommend natural treatments if at all possible. It is better on the fish that is already stressed. Then if natural doesn't work then the heavier treatments can be used. If you would like a full detail description of the mela- or pima- fix treatments, the link below will be helpful.
Melafix and Pimafix

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Phishie
Site Coordinator

"An ounce of prevention is worth a pound of cure."