Need Help With Fish!!!

[mbailey26]

I have a fairly new tank, but it has cycled and all my levels are good. I have had a couple damsels in there for about a week they have been doing pretty good but I just notcied that might striped damsels top fin is deteriorating and his tail looks like it has brown spots. I dont know what this is or how to fix it. I would appreciate any help.

 

[elfdoctors]

Welcome to the Boards!
With a freshly cycled tank, I would be suspicious about water quality issues. The cycle is finished when there are enough bacteria to break down nitrogenous wastes. However, there are many other wastes which may have formed from the rotting which triggered the cycle.
A relatively large water change (~20%) may fix this problem. If not, you should probably treat this fish in a hospital tank with an antibiotic such as Maracyn 2 (unless you see other spots that would suggest a different disease).