How many Barbs are there including if any are Glowfish?
There should be one male and 2-3 females. Some individuals seem to be the worst ones.
If you could set up a QT and medicate the plastic tub or what have you, the rim of white is dead tissue and it seems to be receding nearly to the body of the fish. You still have a chance, but it looks bad.
If you have medication for fin rot then try it in a bucket or plastic tote, if you don't have a QT. Put 100% clean water in each day. Feed then after about 15-30 min, do a water change on the bucket. That way he will be in cleaner water all day until the next feeding.
A 1/4 teaspoon per gallon of aquarium salt to help his slime coat, and Epsom salt / which is not really salt but magnesium sulfate a mineral, a tablespoon per gallon dissolved. Added into the initial QT in 1/3rd amounts over 12 -24 hours. Then just keep adding the total amount to the pwc each time.
You can make up a container of concentrate ahead so you can add just a certain amount of the liquid concentrate to each water change daily.
Ich doesn't eat the fins like that.
You could still have ICH, if you had it before and didn't treat long enough.
Also if the heat is still high in the tank he is in from the Ich heat treatment, higher temps can cause infection to speed up too.
http://www.aquariumadvice.com/freshwater-ich-yuck/