1. Can I get just one or do i need a pair?

2. Is one okay for a nano BC14 if the shrimp are the only things in the tank?

3. Can I use waterchange water from my 75g to change out water in my biocube14? I heard that you're only supposed to feed shrimp one arm at a time of starfish and to make sure the starfish doesnt fowl the water by changing water daily while they feed