Cerianthus is correct.I have a Yellow Watchman Goby,yes they do need sinking
food.I feed mine Brine and Mysis Shrimp,Squid,Formula One,
brine shrimp Plus
Flakes and Shrimp Pellets.Until the Goby is acclimated to his surroundings
it will stay near the substrate or perch on
live rock.It will take a while before
he enters the water column.Even then it will stay near the bottom of the tank.
During the first few weeks it will be timid,you must see that food gets down
to him.Frozen food is best and it sinks.Shrimp pellets are a good way to get
food down to him,leave a few pellets out at a time and they will soften up.
Otherwise he may spit them back out.Put flake food in a small amount of tank
water until it sinks then add it to the tank.Be sure to feed a variety of food
items.Carbon will only take out very minimal to none of your Ammonia.I hope this
will help.Good luck with your Goby.