Well black Aros are naturally more passive than silvers and any other kind. Mine is very used to me, I put my hand in the tank and he swims by and I touch him lol the water is low because he gets excited when I feed him live food he jumps lol
word of advice, use fishing line not rubber bands
one day, I found that a rubber band had broken, and was sticking out of the vent of my parrot...luckily it came out fine bu I'd hate to see a discus or a black arrow go through the same thing