A couple of fish look "blackened, or dirty"

[Fish33]

Ithought I saw a post just like this a while back, so sorry!!! But I noticed that my rainbow sharks' bottom orange fin looks a little blackened, like burnt almost, and a couple of the black skirt tetras look like they have some black spotty-ish coloration around the bottom of their belly. I've never seen anything like it, also its not raised like a fungus or bacteria, just more like a weird discoloration.
Any ideas?

[mrmoby]

I had something like that on my guaramis, a little bit of a blackening. I was told it wasn't uncomon, and not really a problem. I just made sure the water was ok, and made sure i stayed on top of maintainance. It never got any worse, and i think even lessened over time.

[Fish33]

I had thought I saw a post about that... Thanks for the reply. Some of the fish are well over a year old, which isn't old, but I'm happy they are still doing well, I think I am just paranoid, maybe its in my head . Tank is great other than high nitrates, which I think discolored my neons, so that may be the problem ... Working on that!

[mrmoby]

I know, this happened to me a good year or so ago, and I was convinced my water was horrible and had some sort of rot condition. But, everything is good now.