HELP! Blue tang freaking out!!

[Lsufan]

Blue tangs like to wedge themselves between rocks when they sleep or when they are stressed. I don’t know how mine even fits in her spot she sleeps in but when lights go out she backs up & wedges into her spot. In your case it sounds like it is eighther stressed, sick or both.

 

[ca1ore]

Do you say how long you have had the hippo? They are a very idiosyncratic fish, so the behavior you note is not that unusual. A 90 gallon will become too small for it though, and odd behaviors will increase.