Clown's tail is getting smaller

[tzylak]

The tail first had a bit missing at the top, now that void has increased half-way down its tail.
"Nemo" is over five years old.
He is the only fish to have a problem, other 6 fish are fine.
He is the tank bully so it's unlikely for the other fish to gang up on him.
As if he had some flesh-eating bacteria on his tail.
Water is fine: pH 7.8-8.10, NH3 0, NO2 0, NO3 0-1, PO4 0, Ca 360-400, Alk 6-7, 77-79F, Mg 1340-1420 sg 1.022-25

http://<a href="http://s1006.photobucket.com/user/tzylak/media/Nemos%20tail_zpsxbqnfg0h.jpg.html" target="_blank"><img src="http://i1006.photobucket.com/albums/af187/tzylak/Nemos%20tail_zpsxbqnfg0h.jpg" border="0" alt=" photo Nemos tail_zpsxbqnfg0h.jpg"/></a>

 

[Sk8r]

Bacteria infection, serious: needs to be pulled to hospital tank: do not treat in the dt.

 

[PsychoticBeauty]

What kind of invertebrates do you have in the tank? While the tail might be infected, it almost looks like a crab got ahold of it.