Diamond Goby - long term hiding after being active for days?

[squarereefer]

I purchased a 21-day QT Diamond Goby from my LFS two weeks ago. After adding the fish, it seemed healthy and active for about 5 days. It was sifting sand, swimming all around the tank, always out and about. Then the fish went missing for a few days, came back out for about a day but did not seem active or seem to be sifting sand, and now has not been seen for about 5 days. I never saw the fish eat pellets/flakes, and it did not accept the frozen mysis that I attempted to target feed. It did seem mildly interested in Reef Roids while I target-fed corals. I have a tight-fitting factory mesh lid, so jumping is not likely.

I read many posts about these fish hiding for extended times when first added, but this one seemed comfortable and acclimated. At what point do I accept it's gone vs waiting for a reappearance? I am dying to dig out the burrow I assume it's in, but I don't want to cause additional stress if it's alive there.

 

[blaxsun]

I suspect it will come out when it's hungry or otherwise tired of lurking in its burrow. I'd probably just leave it and not cause it any stress.