Fish Pimple?

Can anyone I.D this pimple looking thing on my Nicaraguan? No other fish in the tank has it and it is definitely new on him (within the last week). Should I QT him and what can I do to treat him?

I'm not sure if its a cut from the lava rock, it doesn't look like it but it has happened to other fish in the tank so I thought i should throw that out there.

I didnt do anything except drop a tiny pinch of salt onto it and then just added the normal "dose" of salt into the tank and it disappeared in a couple of days. I think it was a cut from the lava rock because it looked like the scales over the cut were gone