What is this?

[SeaCucumberFan]

Help! My zebra unicornfish got something on his head! I can't take a good pic cuz its always moving. See the black?
https://drive.google.com/file/d/0B0CfL8c-l0BZWUtQVnB3Zkc2X2s/view?usp=drivesdk

 

[snorvich]

A unicorn fish in a 20 gallon tank? Seriously????

 

[SeaCucumberFan]

Sorry... noob mistake... anyway... what was going on? (Dont judge my fish please!)