So what do you guys think, does Giovanni have fin rot, or is he a tail biter? I didnt have a ton of luck determining what it is from google, so I figured you guys could tell me... its developed in the past few days really (his fins are actually tipped in purple, not black like the picture makes it look)... any help would be SO appreciated! Thanks!
I can't quite tell from the photo (I'd say definitely fin rot if you hadn't said the fin tips were actually purple). If he has chunks taken out of his tail and his tail doesn't look too raggedy around them it's probably tail biting. If they're more raggedy looking, it's probably fin rot. Also, with tail biters, they tend to leave bits of their tail sorta dangling off (I wish I had a pic of when Button bit off part of his tail) and a lot of damage will occur in the span of a few hours.
So if it's a chunk out of his tail when three hours later it was fine, he's probably a tail biter and is prolly stressed out by something. If it looks more raggedy and unifromly eating away at his tail or there are pinholes in his tail, it's prolly fin rot. Either way, give him a salt bath to avoid infection.
If his tail didn't look that when you first got him, then it might be either. Try giving him some salt baths and a bit of bettafix, and if you don't see some regrowth in a couple of days/it gets worst... well from my experience, it looks like fin rot because it looks more frayed. Tail biting generally looks more like this.