The fins on my Yellow and Blue Tangs are disappearing/deformed (see image). They were OK when purchased and over the past 2 or 3 months I have seen this problem. There is no indication of a problem other than the fin condition, they are peppy, eating well and I have seen no discoloration at the fin. There is discoloration on the belly of the Yellow Tang but that may be normal, I don't know but doesn't seem to be associated with the fin if not normal. Water chemistry is OK (except nitrates a little high) and have a Cyano
problem but it's being addresses.
Any idea what the problem is, what is causing it and how to remedy it.
Obviously I will not bring back the missing fin but I want to eliminate the cause so it does not progress.