Convict Tang Brown Spot??

[wetlab123]

Hi all, so I work at my university's wet lab. We have a 250 gal tank with two convict tangs, a snowflake eel, a toby, and a butterflyfish. Today one of the convict tangs had this weird brown spot near its tail. Any help would be greatly appreciated. I have looked around to try and figure it out with no luck and have never seen any of our fish get this. The tank perimeters are all within normal ranges and he was eating this morning

 

[beth]

It looks large. Did the spot suddenly appear or gradually grow in to that? Otherwise, how is the fish doing? Eating still, breaking normally? Fast gilling? What is the pH and ammonia levels in the tank?

 

[wetlab123]

It looks large. Did the spot suddenly appear or gradually grow in to that? Otherwise, how is the fish doing? Eating still, breaking normally? Fast gilling? What is the pH and ammonia levels in the tank?

It is large, just a single dot as of right now. The fish is eating normal, it just appeared over the weekend (we don’t go in on Saturday & Sundays) he seems to still be eating normally, the levels were all in normal ranges, the pH was slightly low but I added some pH enhancement.

 

[beth]

It looks like a skin spot rather than a growth. If so, keep an eye out on it to see if it develops more or is adversely effecting the fish. It may be a stress spot which tangs are prone to get. Is that spot erode flesh at all or just a discoloration of other normal skin area?

 

[SALTWAT3RFISH]

That's definitely a curious mark. Doesn't appear to be irritated. Any change in diet lately?