Care is the same as the green scat argus.
If they are the main fish in your tank, just add a bit of marine salt and keep it at 1.003-1.005 (they aren't too particular), mine always did well with that, and maintainace of the tank won't otherwise change.
You definately need at least four. I had a pair of tigers after the third was picked-on to death, then bought another, and eventually had to buy an argus too. Four was enough to spread the aggression of the dominant one. I recommend at least a 180gal for this number, with plenty of decor to break up the lines of sight.
Great fish, enjoy!