Dimond Goby MIA

Bought a Large Dimond Goby on Sunday. It spent all day Sunday making it's home under some live rock, and I saw it swimming around out in the open Early Monday morning around 3 am. Since then I haven't seen it and I haven't even see any signs of it sifiting sand (i.e. sand being expelled in to the water due to it's sifting. Is this fish very shy and takes time before it feels comfortable enough to come of more?
 
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