Sorry if my reply seemed short. But you did ask how to stop the harassment. It would be just speculation on my part to assume it would stop. How are they doing now? True, sometimes a fish will just take a few pokes at another fish, then stop. Some never stop until the other fish is dead. It is unusual for a fish to go into a new tank and start harassing the fish there, but maybe he felt threatened. All fish are different..no way to say really.