Loosing fish dont know why

[gkersten]

Spec gravity is 1.025 . I cant figure it out either . Not all of the fish are bought from same store. My last addition was a yellow tang which is doing great 3 weeks strong eating well etc . What do you think of the crab idea .. ?? B.s or any validity . Do you think the dotty backs could be that aggressive when the lights go out . I dont see any aggression during the day