Twin spot goby??? Got a pic? If it is goby i an thinking they are sand sifters and eat fauna in sand. They are hard to keep. Try blood worms. I had a pair while back that didn't make it. I even went as far as shooting frozen food into sand bed where they sifted. I could be taking about a different fish then you have too. Pods will eat left over food. Detritus too, They are scavengers. They also eat phytoplankton and zooplankton.