i am setting up a new 20 gallon tank. so far all i have is mollies in my other aquarium. i was looking around at pet-smart when an employee told me that if i were to put a silver dollar with my mollies it would nip their fins and kill them. my brother has 2 silver dollars in his 29 gallon with his mollies and tetras and they do fine. will silver dollars kill my mollies? can someone please tell me all the fish that are compatible with mollies and can live in a 20 gallon tank. thank you.