Well thought to post this before I go lay down for the night. I just recently picked up 4 Indo Dats that were about 2" in size. I have them in a grow out tank 55 gallon. What fish is a good fish to put in with them to keep the disputes down?
I usually keep my dats in larger goups, that way the aggression is displaced over multiple fish versus just each other. You can keep them with many types of fish like Fei Fengs, other perch, arowana (be careful with the growth rates though because the aro will easily outgrow a dat and then it would be lunch). I have some geos and jurupari in with my dats and I haven't had any problems.
Good call Gr8...clearly wasn't on point with this one.
I would especially go with long, vertical plants versus the shorter, bushier ones. That way you create more of a natural environment for them and will see their true nature, versus constant fighting for limited hide spots.