What is this on my goby?

[Le Dirk]

I was watching my tank when my shy little goby here decided to pop his head out. When I first noticed the white thing I thought it was just a bit of sand. But then he started to run around a lot and it didn’t fall off. Is this some kind of disease, or a grain of sand stuck up his nose?

 

[Sosuke]

Looks like a bit of sand got on him, although if it hasn't shaken off wait for someone else to chime in with a better id