I would suggest being very careful with the melafix as this is an extract from the melaleuca tree and has been shown to be toxic to mammals and is readily absorbed through the skin (see Villar D, Knight MJ, Hansen SR, Buck WB. Toxicity of melaleuca oil and related essential oils applied topically on dogs and cats. Vet Human Toxicol. 1994;36(2):139-142.
Abstract: "Cases of melaleuca oil toxiosis have been reported by veterinarians to the National Animal Poison Control Center (NAPCC) when the oil was appled dermally to dogs and cats. In most cases, the oil was used to treat dermatologic conditions at inappropriate high doses. The typical signs observed were depression, weakness, incoordination and muscle tremors. The active ingredients of commercial melaleuca oil are predominantly cyclic terpenes. Treatment of clinical signs and supportive care has been sufficient to achieve recovery without sequelae within 2-3 days."
"Toxicity: The most common clinical signs reported to the Animal Poison Control Center by veterinarians with adverse reactions in dogs and cats after dermal exposure of melaleuca oil include ataxia, incoordination, weakness, tremors, behavioral disorders and depression. The acute toxcicity (rabbit dermal LD 50 and rat oral LC 50) for the major terpenic compounds (linalool, ocimene, alpha-terpinene, 1,8-cineole, terpinolene, camphene) ranges between 2 and 5 g/kg body weight, which is considered a moderately toxic range. From a toxicologic standpoint melaleuca oil can be compared to oil of turpentine, which is readily absorbed from the gastrointestinal tract and skin."
Any bactericidial or bacteriostatic medication homeopathic or not will adversely affect the biological filter if it affects gram negative bacteria. If it does not affect gram negative bacteria then then it will not be effective for most amphibian bacterial pathogens.
I would recommend contacting a veterinarian to examine the tail and possibly treat it.
Ed