Coral Beauty Angel - fin problem

[kmw]

Mike, my CBA, was hanging out in a lower corner of my tank last night. When I looked at him, I noticed one of his side fins was stumpy, for lack of a better word. The long flarey portion of it was gone - like a hand missing the fingers. He was in QT for two weeks before adding him to my FOWLR tank three weeks ago.

The only thing I've noticed in the past week or so is that he's got a rock he likes to slide his side along - like he's got an itch he just can't get scratched. I really can't recall if it's the same side he's now got the stumpy fin on.

I'm breaking my tank down tonight because I've got carpet going into the living room tomorrow. So, he and my two clowns are going into a 10 gallon for the overnight.

My tank parameters:
30 gallon
FOWLR , running since December 2004
pH 7.8
ammonia and nitrites 0
nitrates 5
Salinity 1.025

So, what do I do? Could it be aggression from Lulu my female clown (I'm not seeing evidence of aggression when I'm watching and at home)? Fin rot? Something else? QT him to see if it clears up? Treat with something? He has no other symptoms except the stumpy fin - gills/eyes/scales all look normal. He ate like a champ last night when I fed them - I'm at a loss when it comes to marine disease issues. This is my first one.

Thanks!

 

[Steven Pro]

Are there any white growths or red streaks on that fin?

 

[Steven Pro]

By the way, your pH is pretty low. I don't like to see anything below 8.0 and prefer to run at 8.2-8.4.

 

[kmw]

No, nothing out of the ordinary on the fin aside from the fact it's missing part of it. I've had fin rot in my freshwater tank, and I'm not seeing evidence of it here. But, wasn't sure if they presented similarly.