Hey mike, glad to hear he is doing good for you. keep a good shoal of feeders in with him and he will grow like crazy given good room and water....my guy is a little over 6" already and I got him as soon as I saac advertised them...he is in a 220gal by himself and shoals of food...he is not skittish and is actually very territorial and aggressive...he was only skittish when the tank was kept too bright...I keep him in a natural light room and only put a flourecent on him maybe 4hrs a day but keep part of the top blocked out so he can retreat from the light if he wants....he now attacks the glass if you get in front of the tank and will attack feeders if they come within his resting territory....he has shed his teeth now 3 times, this last set is a big set as you can see in the pics at the link below..they are pure white now and just massive compared to his previous two sets...he has also grown 2 fangs dead center on the top that close down between his two bottom when his mouth is closed...a note on color ect at about 5" he has gotten more black and a white edging on his fins as you see in the pics...before this size they were rather transparent with just a hint of color to come.
keep up the updates with these guys

here are the most recent pics of my armatus from river wonders...growing super fast and a beast of a fish already:
http://www.monsterfishkeepers.com/forums/showthread.php?t=89736