A low concentration is ok but you'd be safer with a salt bath (and a little salt in the water any way). A salt bath is 4 or 5 teaspoons of salt (table salt, cooking salt or aquarium salt, not "low"/"low sodium" salt though) in a litre of water. Put the axolotl in that water for 10-15 mins, then take it out and put it back in a tank of clean water with about a half teaspoon of salt in it per litre - it's safe to leave them in that concentration of salt all the time. Don't leave it in the salt bath itself for more than 15 mins though or you'll do more harm than good.
Repeat the bath perhaps twice a day for a few days. It should get rid of the fungus. However, you need to establish what caused it in the first place. I think it's likely, since you live in Australia, that it's too hot in the axolotl's tank and this is the cause. You need to keep axolotls at 24 degrees Celsius or lower. At 25 they will succumb to stress. Keep in mind that it's better to keep an axolotl at 25 or 26 degrees constantly rather than adding ice cubes or such to the water to cool it, which will cause rapid fluctuations throughout the day. So use a more stable method of cooling (frozen 2 litre coke bottle or some such).