It isn't clear in the picture. Is the white stuff fuzzy? If so, it is probably fungus. Fortunately, if it is, there isn't much of it so you don't need to go into panic mode. I repeat - don't panic - you will stress yourself out and your actions will stress your axolotl out. :happy:
If it is only a little bit of fungus, and isn't associated with an obvious injury, then it probably is water conditions. If that is the case, fixing the water conditions will usually solve the problem without stressful measures such as salt baths.
Check ammonia, nitrite, nitrate, pH, temperature. (I suspect at this time of year, temperature is not a problem.) You want ammonia and nitrite at 0ppm, and nitrate below 40ppm. pH is only an issue if it is extremely low. (Naturally high pH isn't a problem - mine are happy at 8.2).
In my experience and that of other more experienced people, little bits of fungus starts popping up when nitrates start rising.
Additionally, I noticed that when I started refilling the tanks with part-unsoftened water, I stopped getting bits of fungus. (We have a water softener - that takes out calcium.) I don't know if there is anything to that, but if you have a water softener, adding back in some calcium is something you might try.
If it is not fungus, but just thick mucus, the same causes are likely - water conditions.
In fact, most axolotl problems seem to be caused by water conditions ...
