When my cory lost his whiskers, they never grew back. I read that this indicates poor water quality and better water and better diet can help. More worms and live food, less nitrates.
Yeah, I think that it generally indicates a lack in the diiet or else high nitrates in the water. Start doing some big water changes and hopefully that will help. My cories are kept with regular aquarium gravel and it doesn't hurt their barbs so unless you have really sharp gravel or sand I doubt they would just wear them off.
one of my spotted cories lost the barbels on one side only, they just slowly got smaller and smaller and then were no more, the thing is i have very smooth small gravel, and all my levels are ok, am o nitrites 0 nitrates 40 (its a planted tank) I could not figure it out, all the other cories barbels are ok, then 2 weeks later a different spotted cory turned completely black, but no other bad signs, he kept eating and swimming normally. He stayed like that for a week or two then came back to normal and has been fine ever since......it baffled me
found pictures
here's its normal colors:
Heres when it turned black (its blurry but you can still see the color)
Its not usually the gravel that causes the eroded barbles its poor water quality and/or poor diet.I got a trilinatus(sp)off of a friend who didnt take good care of his fish and the fishes barbles were almost totally gone, after a few weeks of good water and food his barbles have compleately grown back.