Need help identifying this

[newt828]

My watchman goby disappeared for about 3 days and recently appeared looking like the picture. He was health the last time he was out now his entire tail fin is missing. No other fish have shown signs of damage or disease.

Tanks is a redsea emax 260
PH 8.0
Ammonia 0.0
Nitrite 0.0
Nitrate 0.2
Phosphate 0.0
Calcium 440
KH 11.03
MG 1343

Tanker is about 9 months old other inhabitants are 2 clownfish, halfblack angle 2 yellow tang, dottyback and firefish. Cleanup crew are blue legged hermit crab, emerald crab, nassarius and trochus snails.

 

[smartwater101]

Perhaps he took a trip through a powerhead?

 

[newt828]

Perhaps he took a trip through a powerhead?

I only have the stock powerhead built into the tank so I don't thing he could have made the journey to the back.

 

[newt828]

I have been told finrot but that would be check of a case for it to progress that quick