Saw an interesting article on sand sifting goby care.
Mix a little R/O with a complex frozen food like Rod’s and let thaw overnight in the fridge. Then, using a pipette, draw up some of the slurry and “inject” into the substrate in multiple places around the goby’s favorite spot in the tank. Some of the food is good for the goby, and the rest will bait pods and other sand-dwelling inhabitants to the area the goby can eat.
Repeat this two to three times a week.
I've got 2 (pair bonded Watchman Gobies) in my 90g reef tank and 1 in my 50g FOWLR tank. The pair in the 90 are pretty big and definitely keep the sand clean. They pretty much own the entire sand bed and go where ever they want. The single one in the 50g also does a great job keeping the sand clean. He's a newer addition but growing and doing well.
I just feed both tanks frozen Mysis (I prepare the frozen stuff 2 weeks worth at a time with some liquid vitamins and keep it in the fridge) once a day and a mix of pellets (mysis, seaweed and something else I'm forgetting) also daily. That plus the sand beds seem to keep them all happy.