Shrimp keep going MIA

[ferret]

Same happened to my shrimps. I kept several types of shrimps in the sump (a small group of same species usually 2 to 4 nos. ) and the amount will decrease sooner or latter and there are no fishes being kept in the sump but with a lot of live rocks. Recently I discouvered one of the peppermint shrimp was being attacked by another cleaner shrimp when it was molting and was being eaten.