I can't speak personally on Sajica's as I have never owned them, but I agree with Alexxxxsv14, lots of water changes and plenty of hiding spots is definitely a good start. With them that small, it shouldn't be an issue in a 55g to set up multiple caves and tree branches or limbs for them to hide behind or under. As they get older and begin to pair off you will want to decorate the tank in a way where it obstructs the view from one side to the other (a larger tank may also be needed down the road as well..), but this is for the male and female once they pair. This way they can claim a corner or side of a tank as their own. If their line of sight is obstructed and they can't see all the way to the other side, they won't be able to see the other fish in the tank all day long, which will help (slightly) curb aggression when they actually begin to breed. Other than that, as long as the water is in good condition and they are healthy you should have a successful pair in no time