I was just looking for thoughts in a Goby for my Red Sea 650
I had i think a diamond goby in my smaller tank but he threw sand all over including corals etc so i wanted one that cleans the sand but doesn't throw it everywhere??
It doesn't work that way. Anything that is going to dig will throw sand everywhere.
So enjoy your diamond goby, and don't worry about the digging and so on. Although you could replace the sand with something courser to slow him down a little.
Unfortunately my Diamond goby went carpet surfing from my old tank the day he was going back to the shop so currently don't have one. He did a brilliant job keeping the sand clean but threw it everywhere which was the reason he was going back.
I am just trying to keep the sand white so maybe it's going to have to be a compromise.