Angelfish has damaged/diseased fin please advise!

(sorry, this should be in the disease thread...)

I've had a new 46 gallon bowfront setup for about a month now that currently consists of 4 angelfish and an eclipse catfish (recently gave away 3 rainbow sharks). They've seemed healthy enough, and the water readings have been nice and stable:

Ammonia 0 ppm
Nitrate 5 ppm
Nitrite 0 ppm
Hardness 120 ppm
Alkalinity 145 ppm
pH 7.2

Temp is at 78 degrees F

However, I just noticed tonight that one of my angels has a beat up caudal fin:

(the angel is swimming normally btw - the photo is rotated)

Does it look like it's a disease (fin rot?) or do you think it could be another fish took a chomp out of him (in which case would likely be the eclipse catfish)?

Please help! Thanks in advance for any advice!

Looking around the internet a bit more and I'm starting to wonder if it's fungus.

I'm doing a 50% water change (although the last one was only about 5 days ago).

Might look into rid ich+ or melafix if water changes do not improve the situation.

Also setting up my extra 10 gallon aquarium for a quarantine tank.

I totally agree that I should hold off on using meds unless it's absolutely necessary. Tonight I should have my 10 gallon quarantine tank set up so I may end up moving the angel to that tank.

I've been looking at them every day, which is why I think it is an injury (it happened suddenly). But that weird poofy pom pom thing on its fin looks kind of like other images of fungus that I've seen. I guess even if it is just an injury having the angel in a separate tank so that it can recover is probably a good idea.

Thanks for the advice.

Well, turns out that it was some type of fungal fin rot. I placed the affected angel in the 10 gallon QT, but it did not make it. I was using filter media from my established tank, and the water seemed fine. Then another angel came down with it, and after having a 14+ hour power outage, I've sadly lost that one as well. I've been using Rid Ich+ in the QT, and it seemed to be working. I wonder if the angels went through too much shock/stress being moved into the QT. Both tanks are running at the same temp 78 degrees F.

It was surprising to see how fast the disease was able to take down the angels. Especially the second one. It only took a couple of days once I noticed it was sick for the angel to die.

So far the other 2 angels and eclipse cat are doing fine in the 46 gallon. I'm really trying not to mess with the 46 gallon too much because I think that if I'm constantly doing water changes every day, then that will be hard for the fish to handle (hence the 10 gallon Quarantine Tank). I'm sticking to 30%-50% 1x a week. And I think that is even a bit on the excessive side for a planted 46 gallon.

I did however add a powerhead to the tank to increase the water flow. This is to test the thought that the disease may have been brought about by poor/not enough water circulation. We'll see how that goes.