Black tetras

[JoelB]

My tetras seem to have a dark fungus like coating on their backs, dorsal and anal fins. It's actually hard to tell whether it is internal or external. There is also some dark discolouration around their colour bands.

Now I recall, they have been a little less active for the past week or so. Before this, they were a little aggressive with each other...some minor damage. Not sure if this is relevant.

It's a little hard to tell from the pics.

 

[Fish Room Plus]

If we are talking about black spots on the fins and tail, its encapsulated worm larvae. Prozi-Pro will take care of this. If you cant find, your lps might have parasite guard by Jungle. 1 tablet per 10gal, works fine

 

[JoelB]

When I first noticed it it looked like a covering of soot had landed down on them.

Then I thought it looked like the powdery mildew that some plants get. Mostly on their body, a smudge on their fins.

Now I'm not sure it isn't an internal darkening. The photos don't show a coating but I'm finding it hard to take a good photo.