Dark brown or black spot behind back leg.

Just got two axolotls yesterday. they are adults but I don't know how old.
I have a tendency to aquire reptiles and amphibians from people who no longer want or can care for them, and these are my first axolotls.
The female has a dark brown or black spot just behind her rear leg. It looks kind of like a scab. Is this just an injury or could it be fungus of some type?
I am currently keeping them in a twenty gallon aquarium, and since they have just moved into it I am sure they are stressed. She seems to be eating fine, and I don't want to try the salt bath until they are more settled in. What are the risks of waiting? I would like to send a pic but currently have no camera, sorry.



Thanks for the help.

Risks of waiting include systemic infection, and infection of the partner, if it is indeed an infection. Most fungus is white or light grey. Keep an eye on it, if it gets worse, salt bath right away.