Lawnmower Blenny with No tail

I have had a lawnmower blenny for about 2 months now and I noticed that the tissue on the tail is gone. Then the next day the tail had completly gone away. It is trying to swim, but just hides most of the time. It will come out to eat occasionaly, but not like it used to. Could my Damsles have picked on him or could it be some fish disease? My local FS said that the Damsles were probably picking on him. They don't bother any of the other fish in there. Please help!!

 

Hello,
First off, what size tank?Live rock?Live sand? How long has it been set up? We will go on from there!!

 

I have a 60 gallon, and I have about 90lbs live rock, 60lbs of live sand. It has been running for about 4 months now. I had a bad case of alage, so the lfs said to put a lawnmower in to clean it up. He did great, it was clean in about a week. I noticed about 5 days ago, that his tail was looking strange. Now he has nothing. He'll try to swim around, but doesn't go too far. It looks sad. The overall appearance of the fish looks good, just no tail.

 

Fin rot is often a sign of poor water quality. Being that your tank is only 4 months old you may be encountering some fluctuations in quality. Make sure your ammonia and nitrite levels are zero and your Nitrate levels are low.

J