Please help! What is this!

  • We are currently upgrading MFK. thanks! -neo
I'm not sure what you are referring to. Do you mean the darkish spot on the dorsal (top) side, the frayed fins, or something else?

Also, you need to give some more background on your setup such as: # of fish in tank (and species/sex if possible), size of tank, filtration, how long tank has been set up, water change schedule, and probably the most important are the water tests (ammonia, nitrites, and nitrates). This information will help us to determine the root cause and how to treat the issue.
 
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