Actually, I have both in my tank. They get along great except for when I feed the tank they both come out and ravage for food! The peps stay out of his way though. I do find the arrow really interesting. I can spend hours just watching the arrow crab clean himself and scour the tank for food. I collected him myself and he has already molted twice in my tank. The only problem happened when I recently added some mushrooms and the arrow decided to see if they were tasty. After the first couple tastes he had had enough, THANKFULLY! But on the safe side, stay with the peps.