That's a good size tank for now but the upgrade will be needed eventually. I would think about adding another species or two now just for precaution. If you need to spread the agression out later when the fish are bigger, youll end up having to spend more money on fish around the same size, so keep that in mind. One time I bought 10 Mayan cichlids, all 1.5 inches, only to end up with 3. Since then, I've thrown other species in the tank with new juvies so they have others to get aggressive with and it really helps. When they are bigger and not in the "fragile" stage, you can get rid of the species you don't want. You'll always have 1 fish thats the smallest and gets picked on the most, why not have that fish be a .99 cent convict?