You will want to exchange the blue dolphin for another peacock. They get 9+ inches and are way too big for your 3 foot tank. The peacocks should do ok though in general. You will want to avoid getting males and females though since once they hit 3 inches or so they will develop spawning activity and the males will harass the females to the point of death and fight amonst themselves. They will also hybridize with each other mixing species when they breed is frowned on in general. A typical way to tell males from females is that the males will develop stunning colors around 3 to 4 inches and the females will remain somewhat drab brown or silver in color. A all male peacock tank is spectacular, put lots of rockwork and extra oversized filtration on the tank and keep a whole bunch of males in there. That would be very nice, its hard to recommend just one peacock since they all are wonderful colored fish. PS: OB peacocks the males and females look the same, most of the other varieties are as i described above. You could try to do a single breed of fish with one male and 2 or 3 females , they will likely breed for you , you would just have to be careful the females have escape areas in rock caves etc..