From past experience with my Silver Aro...
It lost 1 of it's barbels, probably courtesy of the Oscar. Mine was about 14" btw. Anyway, what I did was do a 20-30% water change, add half a palm full of salt, something I call green solution(some solution by tetra for cuts and bruises) and ensured that the water condition was tip top until it fully healed.
So far, I've been treating almost any condition you could possibly think of with the above method.
A friend of mine got himself and RTG for $25 cos half it's tail fin was missing. Using the above method, it healed in no time as well.