Yellow watchman goby, conch snails, some sand sifting snails. I always have pure white sand from them. They just turn over the top layer so the algae does not build up.
I never had luck with my yellow watchman but the 2 diamonds I had always were working the watchman I had just stayed by his hole.I have a diamond,elephant snail,giraffe snail and 2 tiger conch's and a sand sifting star and my sand looks great.
I have a yellow watchman and a pistol shrimp that matched up within a day or two of their entry into the tank. I believe the shrimp is the work horse though. They made a nice little hill in front of each of their caves, but the watchman doesn't seem to come our very far from the entry except when i feed the tank. I would like to try a diamond to see if he would move around the tank more.