i dont know about the twitching shrimp, but i remember that when i first started doing this saltwater thing, i added the fish water(from the bag that i took him home in) into my tank. when i did this, my verts would die. turns out, the place i was buying fish from had copper in their fish tanks and i would add that water to my system. very costly and bad mistake.

anyhow, good luck, hope he turns out ok. if so, name him happy feet