My daughter has an axolotl that we have had now for 6 months. He seems perfectly healthy but every while we notice the tank produce small white, thread worms, which get into the filter and become larger and black in colour. I salt soak the filter, clean the tank, and change the water, all of which fixes the problem for a while. I have looked under the microscope and they are parasitic. How do I treat the axolotl without killing it? Aquarium shops are useless as I keep getting given fish treatments which are toxic. Some woman in the shop gave me something but informed me the last person to use that lost his creature - GREAT! Can I treat the tank with something that won't kill the wee beastie?