In the thread titled "Miracles custom 120 rimless reef to discus" Hart24601 quotes Kyla:
"i started tapping on the rim of the tank with my ring during feedings. they freaked at first but within a week they were starting to associate feedings with noise and the tapping was drawing them out with curiosity. for the first time ever i could stand in front of the tank and have them approach me. around month 7 i moved them to the 180g and continued to increase the shuffling and knocking around during feedings until there was no longer any fear of movement or noise.
today i can rap my knuckle on the tank and they rush me for food. no shyness or fear anymore, no dashing or splashing at the top in a panic. the tank is currently covered but at this point i would feel much much safer having them in an uncovered tank."
There's more on that subject worth reading there.