good ol' cyano Q's

[burrows14]

i have 3 urchins in my tank and they do a great job on the rocks but they never move along my sandbed. i was reading up on some sand sifters and was thinking about adding a knobby sea cucumber cause i read that they filter sand thru their bodies. all i have for sand sifters i have right now is 2 sleeper gobies. well i bought 2 and have only seen one i hope the other one is just hiding.