something killing my fish

Question
ok, so I inhereted some fish from a friend of mine, i oridinally had two zebra fish a monster 5 inch goldfish and a red tailed shark.  I also added a blue Beta fish (I know, I know, its not advised)and a chinese algea eater and a long tailed something or other.  Over the last few months the two zebras and the long tailed something or other have been found with the heads chewed off and the tails missing.  I believe its the goldfish.  Its a ten gallon tank but I know it may be too small for him.  He shows some weird behaviors, spitting out rocks swims into a corner and spazzes out.  I wonder if he is killing off the other fish out of a territorial thing or if it's food.  Keep in mind he has only eaten 1 other whole fish (my assumption because I couldn't find him.  Please let me know what you think and what I can do.

Answer
Hello, You are very right in guessing that it is the goldfish, gold fish should really only be housed with other goldfish as they do get quite aggressive, also the amount of waste they put off compared to your other fish is very toxic to non goldfish. Goldfish produce 5x more ammonia than non-goldfish. Which is why sometimes they are called 'dirty' fish and don't do well in bowls, as they are meant to get about 12" long.


The best thing you can do is get a new set up at least a 20 gallon tank with a filter, and put the goldfish in there. You won't lose other fish in your other tank. Another thing you can do is try to put him up for adoption? or if you have a pond...that might work as well.
I hope this was helpful to you.