The sponge filter needs to be run all the time to be of any benefit to the animal for the reasons Mike mentioned. Depending on the water quality you should probably be performing at least one 10-15% water change a week and possibly two. 100% water changes can cause the tank to recycle over and over again which can kill the axolotls. This is why they are not recommended except when it is an emergency.
You need to test the ammonia and nitrite at the very least. And once again what is the actual pH?
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.")
Ed
