Hello, I have a 55 gallon aquarium with 3 black skirt tetras and got 5 neon tetras. I put in the neon tetras and they acted okay, and all day the fish were in the tank with no problem. At night I turned off the lights and went to sleep. When I woke up I checked mt tank and saw one neon tetra hiding and alive, two dead and on the gravel, one stuck in the filter alive, and one was missing. After seeing what had happened I scooped out the 2 dead tetras and unplugged the filter to free the one stuck in it and one of the black skirt tetras swam over to the tetra, ate its right eye, and killed it. I then isolated the surviving neon tetra (witch wasn't picked on before I could get it), scooped out the dead neon tetra and searched for the one who vanished. I couldn't find it. I want to get some more neon tetras but I don't know what to do. Can someone help me?