New fish is being chased?

Believe it or not, this could be jealousy on the part of the bigger fish. A lot of times, fish fight over territory. The reason for this fighting could also be because they are both males and do not get along very well. Sooner or later, the smaller fish might be starved to death by the bigger fish or killed. If you want to save their lives, your best bet would be to release them in their natural habitat. If you can't do that because of what ever reason, buy another tank and separate the fish. Make sure to also give the smaller fish some company if you decide on separating them. Good luck!