The goldfish won't immediately feed from your hand it takes a while to get them used to the idea.
The way I went about it was to hold some flakes in between my fingers and dip them in the water. I would hold them there for a while as the flakes soaked and became wet, and eventually they'd fall out of my fingers and the fish would eat it.
Eventually Lucky would come closer and closer to my hand as she associated fingers with food and after a few days of this she was happily nibbling from my fingers, in fact now she nibbles my fingers checking for food when ever I'm doing things in the tank
With feeding extra food, if it helps, then that's good, but I would agree with testing the water more often whilst doing this, just in case