After adding new invertebrates to your aquarium, specifically crustacean like shrimp and crabs, don’t expect them to come out and stay out for any extended period of time. These inverts normally spend their daytime hours hiding in the rockwork, coming out only at night when their natural predators in the wild would be tucked away and hiding from their own predators. Because of this, you might go days or even weeks without seeing your new crustacean, with the only evidence of their survival coming in the form of an exoskeleton that has been recently cast off during molting. There’s no need to panic if your inverts go missing, and it’s certainly not wise to knee-jerk react to the situation. Don’t tear the aquarium apart looking for the hiding critter, and don’t immediately buy a replacement invert as you may unknowingly overstock your aquarium.