black marks on tetra?

Question

All five of my tetras have black markings on them, these were not here the other day. There are 2 glowlights, 2 bloodfins, and one well I'm not sure what it is (was in the wrong tank I guess) but it is a tetra. They are acting fine otherwise and my other fish don't have these marks/patches. Any clue?

Answer 1

It really depends on the location and size of the black marks but my first guess would be ammonia burns. A good water change would help prevent additional problems.

MM