Is my blenny okay?

[Deadlocked]

Hes been hanging out near the top of the tank a lot the last couple days and biting at his tail at times. My 2 clowns were always swimming together and now one has been swimming separately and darting around the tank sometimes. Does anyone know what the reasons could be? I checked ammonia, nitrites and nitrates. 0-.5 ammonia. 0 nitrites. 20 nitrates. Thanks in advance.

 

[blaxsun]

Mine did this for about a week about a month or so back. He was apparently stressed over the addition of some new fish, so I worked on expanding the rocks around his barnacle hotel and that made him a happy camper.