I also would not suggest two gobies in that size tank unless they are a mated pair. I have two Yellow Watchmen Gobies in my 155 there were "supposed to be" a mated pair, they fought for three days and now live at peace on opposite sides of the tank. Every once in a while (once a month) they do still fight and one will steal the others burrow, but at least there's room to do so in my tank. I wouldn't ever put two of these guys together in a tank 1/3 the size of mine without being absolutely positive that they were a mated pair.
For the record, I have two sand sifting starfish that are out very often. They climb the rocks and glass all morning and late afternoon while the actinics are on and all night. They just don't come out during the heart of the day, but I'm not home then so I don't mind. They're really easy to care for in my opinion. I had both in a 40G, and then now have moved them to my 155G. Do a great job with the sand and are fun to watch. They might not be as fun to watch as some of the more colorful species, but they can be spot fed.