Is my fruit tetra mix agressive?

a few fish had been killed the last 3 days ago like i had 6 fish and 3 days a go 1 was dead yesterday 2 were dead and today 1 i think its that 1 b/c he has been the last one surviving i went to petsmart to tell one of the employees and told him that in a website it said they were cichlids he also told me if i had smaller fish in my tank the fish might be killing it so is my fruit mix tetra agressive then???