I have a FOWLR tank with only 2 clowns and 2 damsels. Recently, I bought a cleaner shrimp. I bought it in the evening and saw it well in the morning. However, when I came back from work, I couldn't find my shrimp. I saw very few pieces of shells on the sandbed, and I thought the shrimp might have shed its shell. But I couldn't find the shrimp the next day, so I turn my LR around and still couldn't find it. What could be the cause of this? I did not see any crabs or mantis shrimp around.