Meg, I would keep him. They are great fish. Give the fish time. They will come out eventually. Like fritz says, your tank is new, and they need time to adjust.
Pink Spotted Watchman Goby
(Cryptocentrus leptocephals)
Quick Stats Minimum Tank Size: 30 gallons Care Level: Easy Tank Conditions: 72-78?F; sg 1.020-1.025; pH 8.1-8.4; dKH 8-12 Max. Size In Aquarium: Up to 6" Color Form: Blue, Pink, Tan, Yellow Temperament: Semi-aggressive Reef Compatible: Yes Diet: Carnivore Compatibility: View Chart Origin: Cebu, Sri Lanka Family: Gobiidae
The Spotted Watchman Goby is also known as the Pink and Blue Spotted, Singapore Shrimp, Leptocephalus Prawn, or Pinkspotted Shrimp Goby. The head and body are yellow to tan with pink spots surrounded by smaller blue spots. It requires a 30 gallon or larger aquarium with plenty of loose coral rubble, ample swimming room, and a sand bottom for burrowing. It rarely becomes aggressive towards other fish, but it is territorial, and will fight with its own kind unless they are a mated pair. It may try to jump out of the aquarium or other small openings, therefore, a tight-fitting lid is required. The Spotted Watchman Goby diet should include a variety of mysis shrimp, vitamin-enriched brine shrimp, table shrimp, and frozen food preparations for carnivores. It should be fed at least twice per day.
I have a diamond watchman goby and he sifts the sand like crazy. He doesn't even eat the food I put out for the fish, he will come out when I feed cyclopeze for the leather and hammer corals. I also see him during the day time on the rocks looking for copods and sifting the sand. He does hide a lot but he cleaned my tank of some serious green algae that was starting to cover the sand bed. In 3 days he did a serious cleanup, I've had em about 2-3 months now. Just my 2cents hope it helps.