i had a strawberry crab for awhile (pinkie) and he had a great personlity, we loved him
but when he molted he almost 3x his size and then he disappered and we never have found him again, when he went missing he was maybe one inch across and i never saw him bother anything in my tank
the horse shoe crab is going to get really large for a 30 and will dig up your sand if thats what you have, they like to hide in the bottom
hope this helps, i would love another pinkie crab, but right now my tank just doesnt seem to do well with emerals or strawberry crabs just my little hermits and my gaint holloween crab seem ok
good luck