I had a Purple Firefish Goby that was always hid inside a cave. Only to show up late in night and then jump back in it cave. It disappeared with no reason (I believe he got stock between my DIY background that got lose and the glass.

I bought a new Purple Firefish Goby. This one is even worse. Since it was dropped inside the tank few days ago, it is hiding under a rock.

I have, clowns, cromis, tang, butterfly. All peaceful and most new addition.

What should I do with this one?
Are they in general always hiding out all the time?

Thank you