i am new to all of this aquarium stuff and just got a 75g from a friend(kept a lot of the water so i think it should only take maybe 2 weeks to cycle?). i want to put a couple of large, colorful, and aggressive fish in there that are social and swim around frequently as well. i was reading through some forums and saw things about cichlids, oscars, and convicts. what is the difference between all of these? i would like to put some bright blue aggressive fish if that is possible. are some cichlids more aggressive than others?