[ChiWing]

You'd have more options if you re-homed the coral beauty. He'll feel cramped in a 30g and may get stressed which can lead to illness and/or aggression. With him in there I wouldn't add any more fish that share the water column. Small ground dwelling gobies are less likely to make him feel like another fish is encroaching on his territory since they stick to the bottom of the tank, so one of them would be your best option currently.

EDIT: sorry, just remembered you already had a goby!