Sorry for your lost..
This is the first time i've heard of Arowana dying from Ick.... I've had tanks where the fish had ick.. and it was fine.. well.. arowana dont usually get ick.. but i guess they can die from it too..
Dont give up.. just remember that whenever u bring a new fish and introduce to your tank.. make sure to put in some ick medication.. I always do that to make sure.