Fins on Tangs

[FireEater]

Both tangs and they are the only fish have what looks to be chucks from their tails and other fins.

The Powder Blue seems to have it only on it's tail, but the Purple Tang has it on every fin.

They are healthy and eat great. This has been going on for a few months now. No other fish in the tank is like this.

Anyone have any idea what this is and how to treat it?

[leebca]

There are, in general, 3 possibilities:

1. Another marine life form is attacking them;
2. They are suffering from low nutrition. They may be eating well, but are they getting all the nutrition they need to repair fins?
3. Water quality.

It could be 1, 2, or all 3.