This will sound quite stupid, but I haven't seen my lone cleaner shrimp. I was out of town last Friday to Monday, made a water change Tuesday, and yesterday, I just realized that the shrimp was missing. I don't remember the last time I saw him - probably two days before I left last Thursday's my best guess. I searched the live rock, substrate --- none. He didn't jump out. I'm careful everytime I vacuum the gravel when I make water changes. It's a 25 G SWFO tank with only 7# of live rock. Fish are a royal gramma, 2 percula clowns, a banggai cardinal and a clown goby.
7# live rock
2 clowns, a royal gramma, a clown goby, and a banggai cardinal
1 cleaner shrimp
blue, red, green crabs
nassarius, astrea, black turbo, margarita snails